That’s a start. Nice.
But this really needs to be a switch that’s flippable on a per-interface basis, and which encompasses the prefixes directly attached to that interface under /ipv6/address. Just like how proxy-arp works for IPv4.
If I have a MT attached to an internet connection that I only get a single /64 on, and so I use that same /64 on both WAN and LAN, an ndp-proxy needs to be able to proxy responses for either side, automatically. If I have to manually maintain a list of individual addresses on the LAN that the MT needs to proxy on the WAN-side, this is not going to prove to be very useful (unless paired with some scripting that can frequently comb through /ipv6/neighbor and auto-populate the ndp-proxy address list with any new entries it finds).