As a consumer I'm excited by the vision these convergent solutions sell, in a futuristic "I just carry one device" way, but I think the reason they haven't kicked off is that in reality you don't just have monitors and keyboards and mice lying around wherever you go.
A significant part of the value prop of the "mobile" desktop is that you can "just plug in", but if you have to carry a keyboard and mouse well you might as well also carry the incredibly thin screen it's attached to on a laptop.
My friend has a foldable screen phone and carries a cute foldable keyboard with touchpad. He can plug in when available or just do light stuff at cafes with the keyboard in his bag
He could instead use a normal phone, but while plugging in display ("AR") glasses from Xreal, which act like an external monitor. He might also want a foldable mouse in addition to his foldable keyboard.
And the phone should be a Samsung, which has DeX (an Android desktop mode). The official Android desktop mode isn't released yet.
I've been diving towards this outcome for awhile now.
I have a gpd pocket 4 for my machine, but carry a chiri CE 5x3 and the MS arc mouse (and am looking for a second screen).
It's an extremely small footprint in my bag, and i'm not sure it can get much smaller. You could remove the keyboard and the mouse from the Pocket 4, but given they're on top of the hardware it wouldn't save that much space.
I can, in theory, do the same setup with my phone instead of the pocket though. I'm yet to really hook it all up and test (I expect several points of failure given past experiments), but the idea really is intriguing.
It does however require people to get more comfortable with smaller keyboards/mice (please for the love of god, if nothing else, swap left control with caps lock), or at least more portable ones.
And as for the ideal of "carry a drive, hook up to hardware as needed", that'll always run into the common issue of who is maintaining the hardware. We need cheap and easy to fix/replace hardware for that to ever really be a thing.