According to Trekcore's facebook page, Unification is getting the special single disc release. The only thing I don't like about that aspect is I will probably not buy the signal disc release and I will miss the special features about Spock. Darn them for that.
"Unification" would certainly sell better than "Time's Arrow" as a single disc release, they can put a nice big picture of Spock on the cover. I can see them doing a new Nimoy interview as part of the extras.
Target will probably have their save $10 deal again when you buy it with the S5 TNG set on release week.