At this point I'm guessing they're going to go after all semi autos.
Don't worry, Taurus has it covered.
*snicker* ... and yes they do make it in larger calibers.
Edit:
Being me, I'd prefer an M1A myself (i'll echo national match plz! hehe)... but that's all just personal mumbo jumbo that don't matter one bit.
Seriously though, AR15 vs M1A, does depend a lot what you're intended goals. Matching bullet termination power with intended target is rather key. Sure, you can shoot a rabbit with a 308, but don't expect there to be anything meaningful/useful left over (pelt, etc). Similarly, putting 223 into a deer is silly (there, I said it. haters gonna hate).
For 308, you can get either gun chambered for it, but the M1A has a very long history with 308, so I'd suggest that.
For 223, the AR15 similarly has a very long history for that round... so I'd suggest a decent quality AR for it.
For close quarters, either will undoubtedly have over-penetration concerns.
If you want to go for distance shots, I'd suggest the M1A myself.... although there are folks that can do well with a well tuned AR.