I still think the Rus lose to the Mongols, united or not. However, it would set a example of unified Russia for others to follow, that could lead some pretty interesting butterflies. Maybe a quicker post-Mongol unification could be on the cards?
I think Kiev would be the most likley candidate, however, as Russian Sailor said, they were in somewhat in the process of their own demise. Novrogod is too busy focusing on the Baltic, and I dont think Vladmir-Suzdal had the strength to acomplish it (though admittley I know little about them). So I think a POD with a more North-looking Kiev is a good place to start.
(Sorry this is quite vauge, I really just wanted to bump the topic becuase it sounds quite interesting

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