From what I've seen and read, granted that I haven't gotten to 50 with my first job so my thinking may very well change, but it seems that for the first runthrough there seems to be just enough quests to get you there, if you can find them. The quest hubs are very sporatic and you are not directed to them, except perhaps by the main questline, but if you are in between, when the quests run out the game doesn't really give you hints as to where to go next. For example, even the new event for Lightning, I was in Gridania and there was nothing to indicate that if I wanted to participate I needed to go to Limsa Lominsa. Something like that should be I think automatic in this day and age.

As for leveling secondary jobs, it is going to be very hard if they don't add things to do. This game isn't built like FFXI, where you can group, find a camp and pull mobs to grind.