I'm planning to keep the basic, most used APIs the same, but yes, there will be some breaking changes. Promises will follow ES6 API and advanced redraw control APIs will likely be changed to improve ergonomics and leverage good ideas from other vdom libraries.

Will there be changes to the vdom structure that might break MSX?

I don't think so. Even if there ends up being one, I'd send a PR to insin. Planning to keep it @pragma jsx friendly, though.