All due respect, built-in superuser is total trash in terms of reliability, compatibility, and UI. SuperSu works incredibly reliably, is recommended by the biggest root-based Apps out there, has a clean and minimal UI that doesn't dominate your screen or make you tap on tiny little bubbles to do what you want, and just takes a quick flash of a zip to get working fully.
In my eyes, it's not a priority and it probably shouldn't be. It's up to Franco though.
Since we are at that, well SuperSU is the best Superuser i have used so far. I have bought it and installed in my prior smartphones and with the CM11S too.
That said, i dunno where you read all that bull**** about built-in superusers and that's highly disrespectful for whoever integrated one.
I'm not here to argue with you, you'll be better served going to the right thread and tell to the CM/PA/Smlimkat team Your superuser sucks bigtime, get a life losers and wait for an answer (if that you like to do in your spare time).
Asking to support built-in superuser isn't an rough remark...
Have a good night.