In reply to Cathy Tibbles.

Yes, there is a block-based themes meeting held by the theme review team every other Wednesday at 16:00 UTC. There should be one this week. The info is available in the sidebar on the Make Themes blog. That would be one of the best places to get a feel for and catch up with what is happening.

Also, be sure to keep up with the block-based themes experiments repo on GitHub. That is where various developers are experimenting on future theme ideas and how they will work within the block system.