One aspect that you may want to consider for enriching the details of your timeline is that of language. The number of languages spoken in the Americas in 1492 was perhaps around 1,000, though it may have been higher (and as always, the boundary between language and dialect is not a clear one). With the gradual agriculturalization, urbanization and state-formation processes occurring in your TL, the number of languages, and the level of linguistic diversity, is going to trend downwards, as happened historically in Eurasia due to the same factors. State societies simply tend to absorb and assimilate smaller language groups, and indeed this process was already underway pre-1492 in the Andes under the Inkas - even without taking into account the further reduction in linguistic diversity that occurred under the Spanish (who actually expanded the use of Quechua for evangelization purposes), the Andes today is a linguistically far more homogenous region than its immediate geographic neighbor, Amazonia, as well in comparison to the likely linguistic state of the Andes itself one or two thousand years earlier. In the modern Andes, the Quechuan and Aymaran languages predominate, a direct result of their use as languages of state power in Tawantinsuyu as well as their post-colonial promotion by the Spanish (though curiously, the once equally-prevalent Pukina language has almost entirely disappeared). Most minority languages of the Andean region are found in the northern reaches of the cordillera, within modern-day Ecuador and Colombia, likely because these regions had been under much more tenuous Inka rule than the broad central Andes and Altiplano, and indeed only one non-Quechua/Aymara linguistic group is still found in the central Andes - Uru-Chipaya, with around 10,000 speakers in western Bolivia.
Mesoamerica on the other hand is an interesting case, because in OTL, most of the original linguistic diversity of the region has survived to the present day, despite the centralizing forces of the Triple Alliance and later New Spain. The main linguistic groups found in modern Mexico are the Oto-Manguean and Mayan families, with a presence in Mesoamerica dating back many millennia, and the Uto-Aztecan family, largely represented by the more recently-arrived Nahuatl-speaking peoples and their linguistic relatives in the north of Mexico such as the the Yaqui and Opata (in the US, the Uto-Aztecan family extends on to include such languages as Hopi, Paiute, Shoshone, and Comanche). Oto-Manguean is a very dense and compact language family, spread across the western and southern parts of core Mesoamerica yet encompassing nearly 200 distinct languages; its best-known members include Mixtec and Zapotec. The Mayan family is of course well-known, and concentrated in the far southeast of Mesoamerica, in the Yucatan and Guatemala, but with an outlying language - Huastec - spoken far up the Gulf coast. Beyond these three main groups, several other small families and language isolates (individual languages with no known relatives) are found. These include the Mixe-Zoque languages of the Isthmus of Tehuantepec; the Totonacan languages of the central Gulf coast; the Tarascan languages; and Tequistlatecan and Huavean of Oaxaca. What's striking about this picture of diversity compared to the relative homogeneity of the Andes is how it likely reflects the governing style of the Inkas versus the Aztecs; while Tawantinsuyu was a unified, centralized, stratified, large-scale bureaucracy, not far off in its governing style (and in its effects on local languages) from the Roman Empire, the Triple Alliance was much more decentralized and less ethno-culturally cohesive, with the result that the pre-existing languages of Mesoamerica were not pervasively replaced with Nahuatl. This is only one aspect of the difference of course; another major difference is that the Nahuas were relative newcomers to their region, while the Quechua- and Aymara-speaking peoples of the Andes had deep roots in their area, likely having a cultural presence in earlier Andean states such as Tiwanaku and Wari.
With respect to your TL, a longer existence for both the Inka and Aztec Empires would most likely lead to the extinction of many minority linguistic groups in those regions under their control. You would almost certainly see a purely Quechua-Aymara(-Pukina?)-speaking Andes up until the fracture of Tawantinsuyu, for instance. I'd stress again that overall linguistic diversity will be reduced as cultures move towards sedentary agriculture, urbanization, and state societies, though this linguistic change will proceed unevenly and quite distinctly in different regions. Look for the greatest reduction in diversity to occur in areas of long-standing state formation, such as the Andes and Mesoamerica, while linguistic diversity will be retained in "refugia", marginal regions of difficult terrain such as certain mountain ranges, dense rainforest, peninsulas, offshore islands, etc. You may also see a partial re-diversification of the Andes and Mesoamerica upon the collapse of the major empires in these two regions with the subsequent infiltration of nomadic groups from the northern deserts and Great Plains (Mesoamerica) or the northern cordillera and Amazon basin (Andes). Depending on the circumstances surrounding the collapse of these major states, you could either have these infiltrating groups assimilate linguistically to the established population (a la the Franks and Goths in post-Roman Gaul and Iberia) or assimilate that population to their own language (a la the Slavs in the post-Roman Balkans, or the Turks in medieval Anatolia).
This is a fascinating timeline idea, I look forward to reading more! Good luck!
Mesoamerica on the other hand is an interesting case, because in OTL, most of the original linguistic diversity of the region has survived to the present day, despite the centralizing forces of the Triple Alliance and later New Spain. The main linguistic groups found in modern Mexico are the Oto-Manguean and Mayan families, with a presence in Mesoamerica dating back many millennia, and the Uto-Aztecan family, largely represented by the more recently-arrived Nahuatl-speaking peoples and their linguistic relatives in the north of Mexico such as the the Yaqui and Opata (in the US, the Uto-Aztecan family extends on to include such languages as Hopi, Paiute, Shoshone, and Comanche). Oto-Manguean is a very dense and compact language family, spread across the western and southern parts of core Mesoamerica yet encompassing nearly 200 distinct languages; its best-known members include Mixtec and Zapotec. The Mayan family is of course well-known, and concentrated in the far southeast of Mesoamerica, in the Yucatan and Guatemala, but with an outlying language - Huastec - spoken far up the Gulf coast. Beyond these three main groups, several other small families and language isolates (individual languages with no known relatives) are found. These include the Mixe-Zoque languages of the Isthmus of Tehuantepec; the Totonacan languages of the central Gulf coast; the Tarascan languages; and Tequistlatecan and Huavean of Oaxaca. What's striking about this picture of diversity compared to the relative homogeneity of the Andes is how it likely reflects the governing style of the Inkas versus the Aztecs; while Tawantinsuyu was a unified, centralized, stratified, large-scale bureaucracy, not far off in its governing style (and in its effects on local languages) from the Roman Empire, the Triple Alliance was much more decentralized and less ethno-culturally cohesive, with the result that the pre-existing languages of Mesoamerica were not pervasively replaced with Nahuatl. This is only one aspect of the difference of course; another major difference is that the Nahuas were relative newcomers to their region, while the Quechua- and Aymara-speaking peoples of the Andes had deep roots in their area, likely having a cultural presence in earlier Andean states such as Tiwanaku and Wari.
With respect to your TL, a longer existence for both the Inka and Aztec Empires would most likely lead to the extinction of many minority linguistic groups in those regions under their control. You would almost certainly see a purely Quechua-Aymara(-Pukina?)-speaking Andes up until the fracture of Tawantinsuyu, for instance. I'd stress again that overall linguistic diversity will be reduced as cultures move towards sedentary agriculture, urbanization, and state societies, though this linguistic change will proceed unevenly and quite distinctly in different regions. Look for the greatest reduction in diversity to occur in areas of long-standing state formation, such as the Andes and Mesoamerica, while linguistic diversity will be retained in "refugia", marginal regions of difficult terrain such as certain mountain ranges, dense rainforest, peninsulas, offshore islands, etc. You may also see a partial re-diversification of the Andes and Mesoamerica upon the collapse of the major empires in these two regions with the subsequent infiltration of nomadic groups from the northern deserts and Great Plains (Mesoamerica) or the northern cordillera and Amazon basin (Andes). Depending on the circumstances surrounding the collapse of these major states, you could either have these infiltrating groups assimilate linguistically to the established population (a la the Franks and Goths in post-Roman Gaul and Iberia) or assimilate that population to their own language (a la the Slavs in the post-Roman Balkans, or the Turks in medieval Anatolia).
This is a fascinating timeline idea, I look forward to reading more! Good luck!