I have lots of thoughts about AR and BR for Halo 4 and in general. Its such a tricky thing to get right, regardless of how easy everyone here seems to think it is. Its not as simple as "just spawn with both". Both would have to be pretty balanced with each other and/or matchmaking really tight to ensure you play against the proper skill group. Neither are exactly easy to do. A skilled BR person will usually beat on an AR user, leaving AR user sad. To balance that you either make AR better or BR worse, which leaves BR user angry. Its not as simple as that though, and I believe they could actually balance both to be effective and liked, but its a fine line and would be quite tricky to do. There's also the matter of "adapt" but let's be real here, many people won't do that, and they shouldn't necessarily half to. They bought the game too and should be able to have fun too.
Which leads me back to matchmaking. Hopefully it works well enough and the 2 guns are balanced just enough that together they work out. I'd like matchmaking to still be fast, but to also better match skills. That's not exactly the easiest thing to do either. Hopefully they'll have focused playlists and game types so that it makes matchmaking more effective. I have hopes they'll pull this all off, but I also know its tricky.