I just want to be able to have multiple, suspendible desktop sessions with different apps running and/or installed and different files available. Ideally I should be able to kick up more than one at a time to let them exchange data. Preferably without having to run a full VM per session. Bonus points if I can ship them between physical machines, though I know that's a long shot.

That's more interesting to me than individually-containerized applications. I want to have per-project and/or per-task-group desktop sessions that are right where I left them when I spin them back up, within reason. That's the one big "killer feature" I feel lacking in every modern desktop OS I use.