I have some relatively big plans for match demos/recordings, so they're definitely on the roadmap. Another benefit that I haven't seen mentioned is that it'll make recording quality trailers a lot easier (I can have full control over the camera), which could be a big boost to marketing/community growth.
Resuming a live match from a demo is probably less likely. In RTS, comp matches are usually 1v1, so it's simply more practical since you don't need to reorganize the same 10 people to resume. RTS games have a lot of details that build up throughout the match (building up bases, resources, units, etc) whereas with FPS games, it's easier to get the match mostly back to where it was by setting a few variables like score... though I guess it will be more complicated for AoT. Not going to rule it out, but it seems like a significant time investment for something that'll be rarely needed.