I've always wanted to see a well-thought out time line dealing with expanding upon Hanno and the Carthaginian exploration of the West African coast.... Carthaginian settlements at Dakar, the Gold Coast, maybe even Cape Town - Mediterranean crops would certainly be suitable to the latter. It would be neat to see trade routes inland, facilitating the Nok culture, Djenne-Djeno, and the Sao (Agisymba) of Lake Chad.
After the Roman conquest of Carthage, the West African colonies might find themselves completely isolated from the Mediterranean world, and it would be interesting to see how hundreds of years of back-and-forth influence between their descendants and the local African populations might speed up development there. Assuming European colonizers eventually show up, we might see some powerful and completely unrecognizable cultures. A hybrid Carthaginian-Khoisan civilization with Mediterranean agriculture and Bantu cattle at the Cape of Good Hope might be situated to benefit a lot from the Age of Exploration.
Also, I'd like to see someone reach Iceland (Thule) in early times - a small, ship-wrecked Greco-Roman trading fleet that becomes stranded and eventually grows to populate the entire island would be fascinating. Perhaps an early Celtic Iceland and Greenland, or a Tamil Australia.
