I don't actually own a Pro 1-X yet (pre-ordered it December 2020)., so I could be entirely wrong on the up-right key. Probably not something I'd use personally.
If any key has to get moved to an unusual space (or require use of up-right_, it should definitely be `~.
Some keyboards also do place \| in the lower left between LEFT SHIFT and Z, so there's precedent there.