The thing I like about the iPad Mini is that it's an optional carry. I don't need an 8" device every time I leave the house. And maybe that's going to be the appeal of the foldable.
Another benefit of the foldable over the ipad mini + regular phone is managing internet connectivity is a lot easier. Also no need for 2 separate sessions on whatever apps/websites you're currently using. As much as syncing states works fine nowadays, it'll never match just sticking to one device and not having separate browsers / note taking apps for your phone + the ipad.
I also don't foresee ipad minis going down that much in size, whereas foldables are constantly being made in smaller sizes (in height, thickness, weight, and even a variety of aspect ratios).
Price is the final real hurdle for most of these things IMO.
In general, managing a single device is always going to be easier than managing multiple -- fewer things to keep charged, fewer updates to run, less stuff to carry, etc.
Yeah, I got used to the big phone, and it's nice to have the big screen around when you are stuck at the bus stop watching YouTube. But I know its an awkward carry for lot of people.
This is exactly why I opted for the iPad Air over the Mini. It's an optional carry device that really only leaves my home when I am traveling overnight somewhere. In that use case, and on my sofa, I appreciate the bigger screen more than any portability advantages.
