The only problem is nobody knows how to make a useful keyboard that fits in my pocket. I hate touch screens in general, but a phone in my pocket is useful in many situations where I wouldn't bring a keyboard.
It should be possible to make keyboard the size of a phone that can be used in the hands. The problem is how to hold it, maybe the iPhone magnets would make that possible. I think the main problem is that everyone is used to using touchscreen keyboard and wouldn't think to use keyboard.
I have an ancient Stowaway Bluetooth keyboard, one of the best folding keyboards made, and I have stopped bringing it along. I found that screen keyboard is fine for small amount of typing. And if I need to do actual work, then laptop or tablet is needed.
It was a far better typing experience than the iPhone SE ever was. Tactile feedback was solid, shockingly so.