Comments by "Laurence Fraser" (@laurencefraser) on "LOST LETTERS OF THE ALPHABET: 9 letters we stopped using" video.

not actually that hard to do, you move one of the punctuation marks under the right hand to another key and stick the thorn there. or employ one of the many ways to give a key three/4 values instead of two (with the letter as the default and the punctuation marks still on the same key, just with a modifier added). programmable keyboards already do this kind of thing a lot (and avoid the issue of backwards compatibility too).
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