Thanks Claude. But maybe we should avoid normalizing ND proxy, lest we end up with ISPs that think it's okay to not provide delegated prefixes? We already have some doing that now; we don't need more.

Note that RFC 7278 doesn't prescribe ND proxy use for the mobile network case. Mobile networks provide the /64 over a point-to-point interface, so they can simply put the /64 and their own address on the LAN interface and it'll work fine, as described in the examples at the end of the RFC.