I don’t think Apple will ever do it.
I personally would like to see the phones behave like iPads when connected to screens and mice and such. I don’t need it to pretend to be a full Mac.
But we all know they’re on the same OS at this point. iOS and iPadOS are completely identical, and this only makes it more obvious.
This is what I want. If the Duo did something like convert into an iPadOS-like environment I’d buy it day one and sell my non-fold iPhone and iPad.
But I don’t want macOS on an iPhone/iPad. If I wanted a device with poorer hardware security that ran an OS with a fundamentally weaker security model I’d just buy a MacBook and be done with it.