First, I wanted to thank all of the Effective Altruism Global organizers and participants. I found it to be very valuable and overall well put together. There was obviously a ton of work put into it, most by conference organizers who I don't believe will get that much credit for it, and I very much commend their work.
That said, there's always a lot of room for new ideas, and I find I often get a bunch of ideas at and after these conferences. Because of the EAGx events, ideas described now may be able to be put into action somewhat soon and experimented with.
As may be expected, I recommend that people make all of their ideas be independent comments, then upvote the ideas that they think would be the most useful.
Lots of small discussion sessions with 6-20 people.
I personally get the most value of conferences from talking to people. One thing I've found works well at unconferences is that there's more socializing during the 'talks'. There have been some small discussion groups; I think these were quite useful, but I feel they often wandered more than they should have and quality decreased over time.
I'd propose something more like there be 20-minute or 30-minute specific discussion groups led by one person, scheduled back-to-back in 5-30 rooms. Maybe some could be exclusive to specific sets of people (VCs, entrepreneurs).
Strongly agree about creating schelling points for specific types of conversations (specific 'topics' might be too narrowing). Simply having signs up in the common area could probably have accomplished most of the benefit for minimal cost.