The Raspberry Pi 3.12 kernel on GitHub has now been updated, and includes a fix for the problem with sdcard (mmc) recognition/mounting..
So.. I now have the Pi running kernel 3.12.0:
Fedora release 18 (Spherical Cow) Kernel 3.12.0-pi+ on an armv6l (ttyAMA0) ................ $ uname -a Linux rgpi 3.12.0-pi+ #1 PREEMPT Sun Nov 10 00:20:34 GMT 2013 armv6l armv6l armv6l GNU/Linux
Robert Gadsdon. November 10, 2013