I just found something interesting:

man 3 gethostid

BUGS
     32 bits for the identifier is too small.

I'll update the get/set hostid functions in libc, and the man page for
same, to use the 64 bit form, and specify that it must beEUI64. I'll pop
some macros for accessing the bits in EUI64s, converting MAC addresses
into them, etc. in unistd.h with the prototypes for get/set hostid()?

The code that sets the initial IP6 address of an interface looks fairly
ingrained, and nobody really cares if the fe80 addresses are made directly
from MAC addresses since they never get stored in DNS or anything, so I'll
leave that be and instead patch rtsold to take a flag (per
interface?) that tells it to use the 64 bit hostid as the EUI64 instead of
copying the address from fe80:: on that interface.

This will make the EUI64-based address assignemtn with rtsold
optional. Nobody seems to be using hostid for anything right now, so
upping ito being an EUI64 shouldn't bnreak anyhting.

Apologies for bad spelling, I'm downloading basesrc, and it's made my ssh
to where I run pine far from interactive :-)

ABS