with recent developments like iPadOS as well as mouse/trackpad support something like this seems more viable than ever before (in a sense iPad + Magic Keyboard is already a thing)

I just realized the iPhones do have keyboard support but no support for the iPadOS pointers yet afaiu (there is some support via accessibility settings though)

Also there are some proof of concept hybrids out there like https://nexdock.com/ and https://www.zdnet.com/product/hp-elite-x3-lap-dock/