Muscowy has in fact already one releasable state: Nizhny Novgorod (2PM if I recall correctly).
If tatar nationalists somehow pop in Kasimov (tatar/muslim province in Muscowy) instead of tatar patriots, then a Qasim sultanate core can be created. Following Danzig example, it's possible that the Qasim Sultanate starts with a 1444 core in AOW. So potentially 2 releasable states at game start.
Finally a Vladimir-Suzdal releasable states would complete the set nicely in my opinion.
Vladimir-Suzdal would be a cool. EUIII also had Murom as a releasable nation.