Private Groups
The problem with communal groups is that things get super generic, attempting to appeal to everyone, and that actually lowers sense of community. They can also be a bit overwhelming for new members. With private, customizable groups, a handful of close friends or even strangers can fashion a space that feels tailored to their interests and comfortable to be at.
The ability to choose to make groups private or public would, of course, aid in a sense of community for those who are shy or only interested in workshopping with a small, familiar group.
Could give the ability to use the feature criteria, only unlocking after posting first work and being a member for a month, for example.
Something like this would be a big endeavor but, in my opinion, also a huge improvement.