He's periodically shown updates on it. From talking to him, there are a number of challenges:

• Being blocked by other features, like a UI refactor
• Compatibility with other existing implementations (less of a problem now with the Group Federation FEP by @nutomic@lemmy.ml)
• Wanting to include Private Groups
• Bringing in moderation, assignment, and delegation tools for groups.
• Dealing with unrelated issues pertaining to the day-to-day maintenance
• Needing to break out new experiments in a branch to see how well an idea actually works

I think the biggest thing is that he probably does spread himself pretty thin at times, and is still learning how to rely on community pull requests and contributions. It can be a really hard thing to do, especially if you feel the need to provide the creative direction for how things ought to work.