I think this makes a lot of sense. We don’t want the instance hosting, say, football communities to be defederated anywhere on account of its users behaving poorly. In general there’s just no reasons to have the users in the same place as the community.
It’s a pretty bold move to launch an open source service like this, especially one that is as complex as a video sharing site. One would think a gradual increase of user base would be easier to handle than a sudden influx of people at a moment when one has been scrambling to meet a deadline.
Good thing they/he is not afraid of postponing the release and making sure it’s ready. And if it works well it will be one hell of a release. Fingers crossed. :)