Maybe not as russian event but as more generally event - east-european lord, who own low-dev prowince, can invite Germans as settlers.
This would be realization of Volga Germans and also german settling in Carpatia and Balkans.
No its too sandbox. Seeing random germanic cultures spawn at random provinces in eastern europe? Does not sound good.
Germans settled in the balkans only is quite small numbers, they were far to have a majority on a territory as big as a province in Eu4.
In Carpathia some Germans were already present at the game start (Transylvanian Saxon), while some moved in after the Turkish Wars. But similarly, the latter weren't really a majority in any region.
In Poland early german settlers probably assimilated by 1400 (around Rzeszów), and they didn't have a single concentration anywhere in territories held by the polish crown.
Czech and Silesian Germans are not represented yet, while Prussia and Pomerania counted as completely Germanic.
In the Baltic the case is similar, cities were overwhelmingly germanic early on, but otherwise not a majority anywhere. Finland had Swedes instead.
So yeah, the only place where it makes sense is Russia.
A lot of germans arrived to other parts of the country too, but only around Kosakenstadt they had a slight majority.
Also as pointed out above, they often came from different places, 'german' being a lumping word for all foreigners, sometimes including dutch, danish, swedish, scottish, even walloon or french.
It would be cool if there was an event for Silesia to turn Saxon, and some better representation for cultures around Prussia.
Also an event for German emigration to Russia and the US for late game.