Another interesting thought experiment would what if we went down to 6 bit bytes instead? Then the common values probably would be 24 and especially 48 bits (4 and 8 bytes), but 36 bit values might have appeared also in some places. In many ways 6 bit bytes would have had similar effect than 9 bit bytes; 18 and 36 bits would have been 3 and 6 bytes instead of 2 and 4 bytes. Notably with 6 bit bytes text encoding would have needed to be multibyte from the get-go, which might have been significant benefit (12 bit ASCII?)

Author here. I agree that this would have a similar effect; we'd probably still end up with 36-bit or 48-bit IP addresses (though 30-bit would have been possible and bad). We'd probably end up with a transition from 24-bit to 48-bit addresses. 18-bit Unicode still seems likely. Not sure how big timestamps would end up being; 30-bit is possible and bad, but 48-bit seems more likely.

Some early mainframes used 6-bit characters which is why they didn't have lowercase.