At max level, I really want to do three things. Solo old content, Raid, and PvP. At first I thought this required three different specs, but now I'm starting to think otherwise and just looking for some opinions from others.

After looking at the PvE Raid specs, I've come to the realization that these would work perfectly well for PvP as well. Considering I'd probably only be doing duels and BGs, a PvE MM spec would probably work just fine. I'd still get Silencing Shot, and the only thing I can see really missing would be Concussive Barrage.

I'm also wondering if BM is really necessary for soloing old content. Opinions on this?

BM isn't that necessary to solo old content BUT it is very useful and helpful. If you use BM spec and a tenacity pet (bears and boars, for example), your pet literally becomes your personal full-fledged tank. It also holds aggro better. I've solo'ed old content on my hunter using BM and MM specs at separate times and BM is way better, in my opinion.

I use MM for PVE (dungeons). I've never tried SV spec yet but a friend of mine has a SV hunter and he claims SV is the best all-purpose hunter spec, is great in raids, and is good for PVPing as well. If this is the case, perhaps try having BM and SV as your dual specs? You'd be a well-rounded hunter this way.

Hope this helps you in some way. Good luck and have fun!

For soloing content, BM is the best by far. However, if you wan't to avoid conformity, try for survival. It's pretty good too for soloing.