To be fair, Apple shot themselves in the foot on the iPhone mini by not realising that that market consists of long-cycle upgraders that product-starved recently went for the SE instead.
As far as an iPad Pro Mini… I NEEEEEEDS IT!!
Seriously, my MBP16 is amazing, and if I'm doing that whole nerdy wannabe IT-ronin programming at a café-thing you wouldn't catch me without both the MBP16 and an iPad (sidecar); but when all I need to do is write an important email, then I'm currently hyperfocusing with just my iPhone (curse you newfangled picture-in-picture!!) and a foldable bluetooth keyboard.
The iPad Mini would have that perfect size for me where I get a slightly bigger display, and yet it doesn't take up any more room than any pocket or mini-bag that currently could hold an iPhone Max can handle.
That slightly bigger display would be absolutely noticeable, and very welcome; but not at the cost of giving up security, or having to use Touch ID every damn time I've spent a few seconds too long without typing.
The only reason why I would buy a future foldable iPhone would be if that's the only way for me to get something that approximates an iPad Pro Mini; but, preferably I would of course rather have a pair of Apple Glass with every app running in a virtual window. *insert Tom Cruise Minority Report-gif*