I mean you can do that with any android and a installed Linux distro. It was also more or less the exact vision of the Ubuntu phone but people didn't care a lot.

The best possibility would be allowing virtualization so you could run iPadOS or macOS (or other desktops), whatever is the best solution for the task at hand.

Doubt it will ever happen though, their restrictions are two decades old and they show zero interest in modernizing them, and have subverted any attempt to force their hand, and those attempts aren't trying to enable this anyway. Triple-whammy.

I used to think similarly, that I wanted one computer in a phone form factor.

I've since changed my mind and don't want one computer at all. I want lots of them, each as isolated as possible and doing a particular task.