I think they need to raise the cap to its max level fairly shortly for 3 reasons:

1) Ps3 needs endgame at release... and if 50 is endgame it is too low.
2) If they do level increases in smaller increments like most mmos do it will negate content.
3) Half the playing population has capped classes, some many capped classes. (you do not want your dedicated players beating a mmo.. that is how you lose ppl)

So they need to increase it to 70-75-99 or what ever cap will be for the next 10yrs. Develop content for it that will be valid for those next 10yrs. So in the end we have an endgame as vast as XI's was with more possible events then any 1 person hardcore or casual could do in a weeks time.

If they leave it where it is... then we will either have a game where content is negated when they increase the cap (the you have 3month of content after an expansion scenario alot of mmos have). Or half the current players quitting because they "beat" the game.