RFC 2782 clearly states that "Clients ask for a specific service/protocol for a specific domain (the word domain is used here in the strict RFC 1034 sense), and get back the names of any available servers." In mDNS, we use a new label "local." and in DNS-SD something more complicated. But those are requirements for protocols, not for built-in stub resolver implementation, API surfaces.
I wonder If we extend LookupSRV to be able to accept an empty string as a local domain or a wild card, what about other lookup APIs such as LookMX, LookupHost? Moreover, what if we extend both LookupSRV and LookupTXT to DNS-SD?
At this moment I have no concrete opinion on this issue, but fixing this issue with #8540 seems reasonable.