Just so everyone here knows, PF is in fact disabled in LFD right now, this is not a level restriction or a quest that is gatekeeping them, its disabled for everyone.
PF was removed from the queue due to rendering bugs causing the ground not to render or something, I forget the actual reason but its been like this for at least a month.
The dungeon is still fully completable if you just walk in, just grab a level 10/11 xpoff buddy and have them run you through. Hell, If you just go to the entrance, chances are you will see low level characters there running it (for reasons I wont go into), I’m sure they wouldn’t mind you tagging along for a run if its just for a quest.
Here: Plaguefall Dungeon Temporarily Disabled
Edit: for anyone that comes across this, PF seems to be back in the queue now.