I'd really like a virtual game space like this open source one (similar to gather.town or Topia), where conference members can walk around, see/hear nearby conversations, and make comments that aren't posted in a giant global chat.

I don't want to be a downer, organizing events is really hard and someone put a lot of effort into this. I think it is worth saying though, the best part of conferences are meeting people, and I feel like solarpunk would emphasize that rather than dimish it. The conference being a zoom call feels a bit, idk, like watching a low quality YouTube video that can't be paused, or being in a big corporate meeting.