It seems to me that there's a lot of unnecessary confusion coming from people not understanding that there are actually two linked but separate mechanisms being talked about here.
One is the SCHED_RESET_ON_FORK flag, which solves the "busy fork bomb" problem. AFAICS this removes the major problem with trusting RLIMIT_RTTIME.
The other is the RealtimeKit daemon, which allows processes to gain realtime priority within the control of the distribution and without the user having to edit nasty config files. It relies on having SCHED_RESET_ON_FORK available, but the reverse is not true.
This makes it a lot easier to accept the two things independently. One is a pure kernel patch, and the other is a userspace control for it.