I don't think I would want this device for $500, let alone what Apple is asking. What is the appeal? There are a few screen scenarios that make sense for my life: (1) Multiple displays at desk to work; (2) TV + couch; (3) laptop + lap or surface; (4) phone (anywhere). I'm never in need of a tablet. If I needed that screen real estate, I'd be reaching for my laptop.
Tmux does not work that well on a tiny screen, and I use it a lot.