I don't think they will do another transition raid. They tried that in Wrath with the Ruby Sanctum and it didn't go over well at all. Basically most raids ran it until they got the achievement (so once or twice, more often than not) then never went back. And people still complained that there was no real content, constantly saying that RS didn't count.
RS didn't count because Wrath's storyline ended with the death of Arthas.
Just like MoP's storyline will end with the slaying of Garrosh. Blizz already said SoO is the final raid of MoP. Anything after is part of the next expansion.