You misunderstood me.

I started off by saying that 0-9a-v digits was "a bit extreme", which was a pretty blatant euphemism — I think that's a terrible idea.

Visually ambiguous symbols are a well-known problem, and choosing your alphabet carefully to avoid ambiguity is a tried and true way to make that sort of thing less terrible. My point was, rather, that the moment you suggest changing the alphabet you're using to avoid ambiguity should also be the moment you wonder whether using such a large number base is a good idea to begin with.

In the context of the original discussion around using larger bytes, the fact that we're even having a discussion about skipping ambiguous symbols is an argument against using 10-bit bytes. The ergonomics or actually writing the damned things is just plain poor. Forget skipping o, O, l and I, 5 bit nibbles are just a bad idea no matter what symbols you use, and this is a good enough reason to prefer either 9-bit bytes (three octal digits) or 12-bit bytes (four octal or three hex digits).