I would second having Optifine available from the launcher. In my case Minecraft isn't really playable on my computer once I go beyond Vanilla. Maybe a check box in the launcher options, or some sort of option in the "Edit Modpack" window. This would make the FTB Launcher even slicker than it already is.
P.S. Of course the FTB team would have to get permission to include Optifine first.
P.P.S. Also, Optifine has the small issue of coming in multiple flavors, which could complicate adding it. Though I suppose if it were just added as an inactive Jar Mod all flavors could be supplied at once.
