The primary, titular goal here is to increase our reliability and kill some resolv.conf config complexity by having internal recdns anycast IPs that are reliable across our network. This also gets us some experience relevant to the (later) task of doing public anycast AuthDNS (parent task).
The simplest way to do this would be to add them as LVS public IPs for the existing LVS anycast services. LVS would still monitor backend pdns_recursor health, and handle BGP advertisements to the routers.
Another route we've been exploring here, however, is to also take LVS out of the picture and have the recdns servers self-monitor and advertise the anycast IP directly. There and up- and down- side tradeoffs to that design decision to be discussed!
Wiki on specifics: https://wikitech.wikimedia.org/wiki/Anycast_recursive_DNS