After D1031 / ports revision 372093 KDE uses avahi instead of mDNSResponder, which according to D1021 might cause conflicts. Therefore we might change the the default choice of the cups port to prevent issues. I'm not removing mDNSResponder because there might be a number of cups users who don't use kde and don't care about it conflicting with the latter.
Unit Tests Skipped
formally there are no conflicts currently: kdelibs depends on avahi-app only, it's avahi-libdns that conflicts with mDNSResponder. If you want change dependency from mDNSResponder to avahi-libdns, please do it for all ports at the same time.
It might be a good idea to ask for an exp-run before committing this one.
I'd like to have more firm data before adding a description like this: everyone who was using the port before and didn't change the ZEROCONF option (most of the people, I'd say) would have had problems by now since we've never used KDE's mDNSResponder backend, and I'd expect at least someone to have sent a PR or posted to the ports ML about this.