but what if,the two phones could be packed into one?

it would be a little thicker, you would need 2 of some components.

switch between phones like switching workspace?

Ha, a phone with a KVM (1) although without the K or M: https://en.wikipedia.org/wiki/KVM_switch

Or this 90's hardware oddity that combined Mac and PC: https://www.youtube.com/watch?v=a6b4lYOI0GQ (skip to 8:00 to see it in action).

I wonder if dual-booting is possible, with the boot-loader loading the bootloader that's been "blessed" by Google's certification priests to boot the "certified virginal" phone.