Assuming by 50th anniversary you mean when Season 1 TOS started in 1966, and not the original pilot, here is what I think will ACTUALLY happen:
1. Star Trek 3 or 13, whatever it is considered.
2. As said before, re-release of previous material on blu ray with the 50th anniversary sticker slapped on
3. Some huge Las Vegas convention with a lot of Trek actors for sure, possibly other large cities, too.
4. As said before, STOGAM\Renegades people produce another online film that includes some lesser TOS actors, and some Trek actors from other series willing to participate
5. a lot of fan films released online
What I would like to see:
1. and Enterprise miniseries or movie, online (IE Netflix) to give it a more proper send off, that includes the Earth Romulan war. (Won't happen, though)