Zeroconf (powered by Avahi/Bonjour) is increasingly becoming the de facto standard for network service publishing and discovery. With all major Linux distributions shipping with Avahi, Mac OS X shipping with Bonjour since v10.3 (in 10.3 it was called Rendezvous), and Bonjour for Windows available, support for Zeroconf is far and wide.

Because ioquake3 is moving to support more generic libraries, such as OpenAL, SDL, etc., it would make sense to move to Avahi and Bonjour for local game server discovery, rather than Quake 3's custom discovery.

Quake 3's custom discovery has a disadvantage in that it only works across the current subnet. If the PC can send traffic to another subnet (via a router), the user can directly connect to another game via the IP address, but it cannot discover the game automatically.

However, if Avahi/Bonjour are configured to publish to a centralised DNS-SD server, local game servers from other subnets can be discovered. (Not 100% if Avahi has this implemented yet, but Bonjour should be able to do it.)

I am not sure about Bonjour, but Avahi is generally accessed via D-Bus. Implementing Avahi would add a dependency on D-Bus, but D-Bus does not need to be accessed directly -- Avahi provides a C API to wrap around the D-Bus interface.