Having to explain federation is kind of the issue in my opinion. This idea wouldn't be to remove the normal sign up process, it would be a way to side step it entirely for those who don't care about the technology aspect of it and just want to be part of the community.

If you want to pick your own instance or suggest one, that would still exist. This would just be an alternative. It would also help to avoid everyone gravitating towards the largest instance, because it would try to load balance people automatically.