Russian separatists in Ukraine have had an important role in "inviting" Russia to invade Ukraine. In order to predict future steps that may be taken by Russia, it may be useful to know: are there substantial groups in other East European countries (particularly those bordering Russia or Ukraine), that support accession to Russia? If so, what are they?
Moldova (which borders Ukraine to the West) definitely has them. They have a self-declared republic there too, Pridnestrovian Moldavian Republic (PMR), better known as Transnistria in the West.
It's more debatable if the Russian minority in the Baltic countries (~20-25% of the population in two of those) could count as such, but relations with the majority there have been tense at times and...
Latvia and Estonia designated Soviet-era migrants as non-citizens.
Contact between Russians and Estonians is rare.
A New Law In Latvia Aims To Preserve National Language By Limiting Russian In Schools
This by Western mainstream media accounts. You can only imagine how the Russian media portrays these matters.
Georgia also needs to be mentioned: Wikipedia on South Ossetia.
Specifically regarding your question: Plans of integration with the Russian Federation.
I almost don't dare to try to write what the Wikipedia link says so it becomes a real answer, but the situation there is a lot like Crimea. (Smooth military operation to take it away from Georgia; if there was election then a big chance they would choose Russia.)