Bavarians can unite Germany, why not then make Lithuanians unite Eastern Europe? At least, most of it.
In the 14th and 15th century, the Grand Duchy of Lithuania was the largest nation in Eastern Europe, if not all of it. Using the situationof a weakened, disintegrated and splintered Kievan Rus' after the Mongol invasion. Mongol "vassalage" was not very strict, so with a strategic usage of marriages, wars and alliances, Lithuania multiplied in size many times, and became a serious contender for the successor to the previous Eastern Slavic state. Not to mention that they could beat the Mongols themselves - Battle at Blue Waters, 1363, 17 years before Kulikovo. The pagan realm was quite literally trying to become an empire.
Both Gediminas and Algirdas, two of the most well known and influential Grand Dukes if Lithuania, agitated for their ambition to unite all Rus lands. They both wanted to rule over all of former Kievan Rus', and this, obviously, clashed them with other Russian states, like Muscovy. By 1368, there was not much left to stand in Lithuania's way. Kiev has been subjugated after Blue Waters. Tula and Ryazan are either dynastically tied to the current Grand Duke, Algirdas, or allied to him. Lithuanian-supporting knyazes are being elected in Pskov, and Novgorod is in their sphere of influence. Only Muscovy remains.
And then...
Wikipedia page for Algirdas wrote:Algirdas occupied the important principalities of Smolensk and Bryansk in western Russia. Although his relationship with the grand dukes of Muscovy was generally friendly (demonstrated by his marriages to two Orthodox Russian princesses), he besieged Moscow in 1368 and 1370 during the Lithuanian–Muscovite War (1368–72).
Lithuania wanted to place Mikhail II of Ryazan on Muscovy's throne. Sounds innocent at first, until you remember that's how the Balts did their jobs. Fighting in Russia was dangerous, so Lithuanian Grand Dukes resorted to dynastic ties, inheritances, and placing their family members on the thrones of Ruthenian principalities. Mikhail was Algirdas's son-in-law. Coincidence... no.
Lithuania wanted to subjugate Muscovy just like any other Russian realm. In fact, it was their last major rival. All other Eastern Slavic principalities were too weak to challenge the Baltic pagans, and Novgorod can't do shit. However, they stumbled across a major problem... Moscow had just built the Kremlin, merely four months ago, and it's thick walls and defenses were not so easy to push over. Algirdas just looted the countryside and returned home. Then he went there again, nothing changed. Algirdas then died in 1377, his co-ruler Kęstutis died soon after from Jogaila choking him to death in prison (All Gediminids were kind of douches, to be honest), Lithuania went into civil war, then Christianization, Polonization, Muscovite-Lithuanian Wars in the 15th-16th century, Russia formed, Union of Lublin, Partitions of the Commonwealth, Russian occupation, all of 20th centuey and we get what we have today. Russia, the direct child of Muscovy, is a major power, a member of the Security Council and largest nation on the planet by landmass, while Lithuania is a tiny speck on the map of Eastern Europe with a history they are overly proud of.
So what if we change that? Let's say the Kremlin is delayed in construction time, or Algirdas actually brings siege engines and takes it down. Either way, let's assume Moscow falls and Mikhail II is put to the throne. For the sake of argument, he dies early, Algridas uses the claim and takes over the Muscovite lands.
I won't try to put up a full scenario (10 PM here, god dammit), I'll leave you to discuss what woukd happen. But here are some things to remember:
1. Revolts against the Lithuanian rule are possible, but unlikely. Sure, you have a different religion, but Ruthenians were under Baltic rule for centuries, and no clashes between the two are known.
Wikipedia page for Ruthenian nobility wrote:It is estimated that by the 16th century 80% of feudals on Belarusian lands were of Ruthenian ethnicity and 19% of Baltic.[16] No major conflicts between Ruthenian and Baltic szlachta of the Grand Duchy of Lithuania are known. Equality of their rights was also guaranteed by the Lithuanian Statutes of 1529, 1566 and 1588. As time passed, the differences between Lithuanian and Ruthenian fractions of the nobility of the inside the Grand Duchy of Lithuania practically disappeared.
Lithuania was incredibly tolerant of foreign cultures and religions. Jews had lived there since the 9th century without problems (aside for Alexander Jagiellon, but nobody likes him), German Christians could freely live and work there, Lithuanian rulers even ordered to build a church in their neighbourhood. A pagan nation building a church - crazy, I know.
2. Siberian colonization is less likely. Lithuanians did not have that much of a culture for expansion and colonization as Russians did. The entire Cossack colonization thing was a Russian thing, and Lithuanians were more used to conquering and looting actually settled nations. Of course, it coukd happen, assuming Cossacks are still a thing and Lithuania tries to sway them back.
3. Lithuania was far more open to Western culture and influences than Russia. It's both living closer to them and interacting to them more. Jagiellon rulers in Lithuania actively promoted the Renaissance. First university in Eastern Europe - also in Lithuania, 1579 in Vilnius. Before the Polish-Lithuanian Commonwealth, serfdom wasn't that much of a thing too. Sure, the peasants had to work for their liege, but they could freely move from one place to another, or just settle a new area entirely. Just that being next to a castle was far safer.
4. Conversion to Orthodox? Not really. Ruthenian and Lithuanian nobilities merged, but for the most part, Baltic nobles held tight on their religion, whether pagan or Christian. Considering the Teutonic raids, Catholicism is still the most likely option, though considering Lithuania's power at this state a union with Poland is unlikely, and Louis II's descendents end up placing a personal union with Hungary.
So, NSG, let's discuss! I myself believe a Lithuanian Rus would end up as a more innovative and Catholic, though deeply split not-Russia, just far cooler. I'm biased, dammit - I am from Lithuania!
I would accept a piece of Lind to start up my empire.