90% of the people who use tablets I know (including myself) only has four use case: watching video, reading PDF and comics, taking notes, and playing mobile games.
All of which are very mobile-oriented tasks that are done on tablets solely for their screen sizes. With trifold bridging the gap between screen sizes and, more importantly, screen ratios, I would love to merge them into one device. This is in contrast with laptops, whose differences in OS and use cases are, to me, much bigger and necessary.
Of course, right now they are very much afar from consumers' pockets due to price and reliability. But normal foldables were once in the exact same state, and the fact that Apple is releasing one soon is a sure tale sign of the future of foldables.
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.
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.