I've been doing all my significant typing in landscape. Occasionally I'll type a word or two of a search in portrait with one finger but otherwise it's the landscape keyboard.
So I decided to type this reply with two thumbs in portrait and I've been surprised at now close it is to working. Unfortunately the centre of the keyboard is too much of a stretch for my hands, but not by much. If the screen was 20mm narrower or if there was the same size gap in the middle of the keyboard then I don't think I'd have a problem.