So you're proposing a Slavic state with a few golden horde trappings? The population balance will tilt in the central Russians favour over time, and you'll have a situation just like China. Plus there are the religious issues with such a scheme.
Is it at all feasible for the Golden Horde to go Orthodox rather than Muslim?
Removing Timur probably helps: he gave the Horde quite a pounding. In the absence of the Timurid states, a Golden Horde that extends itself south and East into central Asia has a stronger settled, agricultural demographic base: pure steppe empires don't do well against early modern gunpowder empires on settled territory.
Now, if they can play divide-and-conquer among the Russian states, they can probably keep that flank secure for a while: Moscow didn't really take off OTL till the mid-1400s, when the Golden Horde had already partially disintegrated, losing Kazan and the Crimea by 1450 and by 1480, when Moscow defied Horde demands for their traditional tribute, Astrakhan also had broken off. A Horde-Novgorod alliance? Or a Horde-Novgorod-P+L alliance?
Of course, if we bump off Timur, the Ottomans are invading Italy or central Europe by the mid-1400s, and the butterflies are huge...
Bruce