Ideally, a bit like the Reach beta where they had a few competitive maps and a co-op / firefight mode. So translating that to Destiny, do something like the old russia area, with a couple of public event spaces, maybe 10 events to cycle in those spaces and one or two competitive arenas for people to drop in and out of. Core focuses would be on networking, weapon / space magic balance, loot / stat progression, competitive multiplayer balance. It's a pretty huge step for them and I would hope they take the chance to run a public beta to stress test everything.