Funny, I'm thinking the same thing......
All rank 50 abilities are obtained through a quest, we already know this. This only leaves 3 options......
1) the quest stays lvl 36
2) the quest is remodeled to a higher level
3) a new quest is rank 50 to learn it
So for them to prevent you from using it, they would have to
1) make it required rank.
2) do another quest