But for an IPv4 device I only have to remember one number :) And nothing to do with a long random serial number.

<prefix>::1, <prefix>::2, <prefix>::3, <prefix>::4... exactly how hard can that be?

Or if you're feeling playful, <prefix>::b0d, <prefix>::bed, <prefix>::dad, <prefix>::b1d...

The prefix is too long and it's not the same at every site.

When I'm at a different location, the biggest problem is usually figuring out if they use 192.168.0 or 192.168.1 :)

lucky you, IPV6 indeed uses the same prefix everywhere: fe80::

Nitpick: The subnet fe80/10 is for link-local addresses (https://en.wikipedia.org/wiki/Link-local_address#IPv6). However, it is not an analog to the RFC 1918 IPv4 subnetworks.

192.168/16 is a private IPv4 subnet (https://en.wikipedia.org/wiki/Private_network#IPv4) and the equivalent for IPv6 is the fd00/8 subnet (RFC 4193).

And with ULAs (fd00::/8) you can pick your own prefix. Officially you should pick a random one to prevent collisions when you connect private networks, but you can choose something memorable if you don’t care about that