Which countries have Russian roots? I'm not aware of any.
You could say Ukraine has Russian roots in that it split off of the Russian Empire and then the USSR. You could also say Russia has Ukrainian roots because that was the historic domain of the Kievan Rus.
Similarly, you could say Bulgaria has Russian roots because it gained its independence from the Ottoman Empire in the 19th century in the wake of the Russo-Turkish war. Alternatively, you can say Russia has Bulgarian roots in that Cyrillic was invented in Bulgaria in the 9th century and spread to other Slavic cultures.
The bottom line is that Eastern Europe and Russia have, for better or for worse, strong historic and cultural ties.
However, the wall did come down. In many places that were on the east side of the wall, people take offence of the name "Eastern Europe" as they feel it refers to bad times they had and they want to get rid off. Rumanians and Ukrainians are all Central Europe, and they will refer to Georgia as Eastern Europe. I am not sure what Georgians think of the name.
It is a bit like some Irish taking offence by Ireland named as one of the "British Isles". That name is a reference to a past they want to get rid off.
I'm not convinced about Russia joining the EU in 50 years; Putin is only 68 and can be reasonably expected to live another thirty-ish years. So we'd have to wait for him to die and the subsequent power consolidation within Russia.
There's a good chance that this point specifically would be why the Baltic states would oppose Russia joining the EU. Take a look at this table:
https://en.wikipedia.org/wiki/Demographics_of_Estonia#Ethnic...