A properly built tablet OS UI would also have those differences in the OS that make it more than just a larger phone screen, which so far seems to be most of what the foldables are doing with a gimmick thrown in here or there.

iPadOS may not fully be to the point of being an OS UI that really utilizes the benefits of a tablet sized device, but it does have elements that are unique to it that would not really make sense on a phone.

That being said, if your tablet use case really is just a larger phone than a foldable would be great. But i know for myself the way I use my iPad it would not be a suitable replacement. Especially not now, maybe in 5+ years once someone figures out how to make an OS that actually manages different ways of interacting with it in different form factors work, but that has yet to happen.

IMHO technology (and price) is just not there yet. I can buy a phone and 2 tablets for less month than a foldable.

I'd love a 10 inch screen in my pocket but maybe in 2035. Nokia imagined this 20 years ago and we're barely there yet.

I wouldn’t put too much hope into foldables, at least not because of Apple’s involvement. They also released the Vision Pro. And there’s still the unsolved(?) problem of the screens getting easily scratched/destroyed if they’re not heavily protected and kept clean. (There are some informative teardown videos, e.g. by JerryRigEverything.)

I can get a foldable phone that extends to a 13 inch screen.

I’d rather have no moving parts in my screen.

I have a hard time justifying buying a trifold when my 13-inch iPad Pro was 1263€ and the Samsung trifold is probably gonna be closer to 3000€ for a 10-inch display. If I assume that it'll be 2999€, you can get a 13-inch iPad Pro (1519€), a Magic Keyboard for the iPad (399€), an iPhone 17 (999€) and still have money left over. And this is straight from Apple.com. It's possible to get better deals elsewhere.

Dunno if Apple's foldable will support Apple Pencil. (For that matter, not sure a touchscreen MacBook would either.) That's one use case for a properly rigid, solid, flat surface.