Apparently people now try to do some things across DBus that require a higher data rate and lower latency than the traditional "huh, somebody plugged in a USB stick / wants root for aptitude/yum / left fpr lunch" events DBus handled in the past.
Newfangled stuff like multi-touch. Or keyboard input (for Chinese and whatnot).
You don't want that stuff to go through more context switches (and processes) than strictly necessary. So AF_BUS seems to be a Good Thing.