You'd be surprised how many cheap tenda wifi "access points" sold right now for 15€ still don't support v6, even though access points shouldn't mess with anything above L2.
Same reason cable modems don't mess with anything above L2 but are still reachable at http://192.168.100.1/ (no IPv6 equivalent).
Isn't that what fe80::/10 is for? (Or ff02::1 but I grant that's harder to use)
The closest analog would be something in fc00::/8 (which belongs to fc00::/7 which is the IPv6 analog to 10/8, 172.16/12, 192.168/16), but good luck getting cable modem firmware vendors to all agree on which random address to use within that and then actually implement web administration and diagnostics on it. That's what I was getting at by saying there's no IPv6 equivalent; they haven't done that.