The idea of having both an iPhone and an iPad in the one device is appealing.
However . . . the iPhone uses the A chip running an iPhone OS and the iPads are predominantly using the M chip along with a slightly different iPad OS with iPad tweaked versions of software also available on the Mac OS but not also available on the iPhone. The pro iPads have 4 speakers which the iPhones clearly don't.
The other issue is the opened tablet screen ratio is going to be 1:1 which isn't going to handy when watching films, or trying to doing video editing. Will you get stage manager with extended display output currently only available with the M chipped iPads? Those with the A chips like the iPad mini 6 and 7 only give you duplicated 2nd display and if the ratio is 1:1 in iPad mode on a predominantly 9/10:16 ratio monitors that's not going to go down at all well. How would such a device integrate with the Mac OS for example?
A tri folding device resolves the ratio aspect somewhat when unfolded but adds complexity. Expecting the front screen to behave like an iPhone and opened to behave like an iPad with the iPad OS - much as I would love the idea; it's as likely as touch input on the Mac OS happening.
Those expecting the impossible, are the ones more likely to be highly disappointed.
An Apple flip phone has merit, a folding iPad so an 11-13 inch display that fits into a cargo pocket the iPad mini fits into but no front display, likewise.
Don't get me wrong, if anyone can Apple will be able to; whether they will and want to is another matter.