It depends. Perhaps not full-blown DNS server, because then people could expect things like DNSSEC and everything. And yes, it might look like too much for router. Although with "it's more than just a router" philosophy, I can surely imagine it as separate package. I'm just not sure if there's enough demand for it (and I'm leaning to "probably not"), to justify making it.
But if it's about adding support for static records of few other types, in addition to already supported A and AAAA, then why not? Almost everything is there already, the whole DNS cache, concept of static records, ... All you need is one programmer who doesn't feel like doing anything big after dinner and he can write the rest before he goes home.