When I've used my rifle in skirmishes (just one larger one outdoors so far this season...indoors/CQB we shoot real cap) I don't find the 30rnd to be a handicap that cannot be overcome with thoughtful game-play. Most quick sets you rarely end up going through more than a couple of mags anyways.
You can't sit back and "rain" BBs onto someone...you just don't have enough ammo to last long doing that.
Best performance comes with semi-auto...so I tend to just double tap shots...and because you're not cutting loose a swarm of shots you tend to aim/pick your shots more carefully.
You can't trade shot for shot with someone not loaded real cap...at least not for long. You need to displace or else coordinate someone(s) else in to work things out.
All in all sounds like a win to me. But blazing away with thousands of rounds on tap (10 mags @ mid cap loads) is fun too.
Haven't seen it in person yet..but the Open Bolt vs Brass Tube use different feed lips and top seals. There'll be mag conversion kits too. I think we'll see a standard sort itself out soon.