Some speculate that Putin might want to turn this paper union into reality before his term ends and become president of the union. He would avoid neatly term limits for Russian president.
Fast forward to 2019, recently the Belarus' ambassador to Russia said that the presidents of Belarus and Russia approved plans to establish a common government and parliament. 
Their plans seem to be progressing. December 8th should be some kind of proclamation about the state of the union.
Belarus is just one military exercise away from Russians taking over. Every time these countries have a big joint military exercise in Belarus there is possibility that Russian troops might not leave when the exercise is over.
Why they would do that? Unless you organize a pro-West revolution like in Ukraine. It is possible but making people dirty poor and desperate can take a decade like in the latter case.
No it doesn't. It's by far the most likely outcome going forward.
"Putin’s Retirement Plan Depends on Belarus"
"To retain power, he is positioning himself as the leader of a closer union between Russia and its dependent neighbor."
That is by Leonid Bershidsky, one of the best columnists in the West re Russia. He essentially never strays into conspiracy theories or similar junk.