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.
Which you commonly have in your pocket? I have a GPD pocket 4 and love me some portable laptops, but I do sorta hope we get somewhere with foldables to where I'm happy just breaking out an arc mouse and small keyboard and treating that as the computer.
We're obviously not, and i'm probably not anywhere near willing to shell out the cash for this, but "the tool you have" and all that.