To be fair, community can and does develop without usernames at all, it's just that people aren't on a personal basis with one another. To be honest, I recognise or even look at most usernames and I doubt many others do. It's similar to reddit, in which someone's username will only be noticed if they are extremely popular (very rare) or have a novelty username.

The effect is lessened here because the prominence of one's posts is not tied to how many points they have (like on old forums) because a person's points are not immediately visible. But anonymous messaging with optional usernames works just fine as seen on 2channel, 4chan, 8chan and the 'old chans' (now defunct).

I don't think community is at all dependent on usernames being used or not.