I didn't read this...
But I would love to see a revisal of the Polish-Lithuanian "empire". I've been thinking about this the past few months.
There's Poland, Lithuania & the other Baltics, Ukraine, could probably add at least Moldova, Romania, and Slovakia. Call it the Western Slavic Confederation (I'm guessing it's pretty similar to the Visegrad Group above, without reading... and, although the Baltics aren't Slavic, they were a part of the old Polish-Lithuanian Empire so I am honorarily including them here...). It would be missing Byelorussia, and Kaliningrad. But go ahead and kick the Russians out of those two areas, and might as well do Transdniestra as well. I'm certain the Russians would love that idea.
The Czech Republic could either lean towards Germany (language/ cultural affinity in western Czechia) or the Western Slavic Union (eastern Czechia is Slavic, like it's former union state Slovakia...). I'm guessing they would choose Slavic based on current political affinities (heavily anti-Russian).
It would also be missing southern Slavic nations but it's a little more tricky down there (Serbia, Hungary, etc...).
But I agree, a mini-NATO in the east of Europe. I think I proposed a confederation with Poland and Ukraine several months back as a pathway for instantaneous inclusion of Ukraine into NATO.
But revising Poland-Lithuania, or creating a Visegrad group is an excellent idea.
Now just...
"March on Minsk" (future victory song of the Western Slavic Confederation!)