8 versus 16 bytes barely matters for using the addresses, especially because if you're assigning IPs to your devices you can have the second half of the address start with 6-7 zero bytes and collapse them all with ::
And I challenge you to name a way to be "somewhat backward compatible" that would actually function and IPv6 doesn't already do.
Edit: And not only can you make your own addresses short, if I look up some IPv6 addresses meant to be said/remembered (public DNS IPs), none of them make you type more than 8 bytes (and that one repeats a cluster to make it easier) and some make you type as little as 4 bytes.
Remembering and communicating mildly complex byte sequences should be an issue which is solved already.
It is solved already, it's called DNS.
IPv4 addresses are not any more difficult to remember than phone numbers, but the same can't be said of IPv6.
The other 4 billion people on the planet don't really need internet connections do they?
Doubling the address space is a good strategy when you need more. Quadrupling it is over-engineering.
64 bits are already a pain in the ass to remember, and if you have specific memorization needs you can use small static IPs so that even with 128 bits available you only use about 64 of them.
New L3 protocols on the Internet are firmly on the "incredibly difficult and time consuming" side.