In some ideal world IP values vary between 0 and 999 and you just add a new block if you run out of them, `999.999.999.999` would be the last standard IP, simply add another `.000` block and you get some more billions IPs.

Having letters in IPv6 feels wrong, at that point why not just have words, reinvent DNS at a lower level. You are already living on Cherry Picked Street, number 15, let your computer have the IP `cherry.picked.15.1`.