libdbus can be implemented on top of the kernel support. What says that you couldn't fall back to the current implementation if the kernel support is lacking?
Kroah-Hartman: AF_BUS, D-Bus, and the Linux kernel
Posted Feb 10, 2013 14:15 UTC (Sun) by tzafrir (subscriber, #11501)
[Link]
But that's legacy code. Who would bother maintaining it (not just the extra code and ifdefs in libdbus. Also the dbusd)?
I managed to keep using that old a kernel version by ignoring the minimally-required kernel image version required by Debian. I ignored it as it was generally a requirement of udev and I did not need udev on that server.