> I still don't understand why they shifted from 0:: to ffff::
I think the most reasonable explanation is probably because they thought ::1 being loopback (otherwise it would have to go above 255.255.255.255) was more important (since it would exist as long as IPv6 does) than the transition encoding that presumably would die off over time.
I think the most reasonable explanation is probably because they thought ::1 being loopback (otherwise it would have to go above 255.255.255.255) was more important (since it would exist as long as IPv6 does) than the transition encoding that presumably would die off over time.