Honestly while I can understand peoples' trepidation on new jobs being locked behind the expansion I look at it like this:
We've just gone through nearly two years of roughly same old, same old. And while Ninja was a welcome refresher for some, think of it like a reward for those who stuck through it and completed it. Much like a job you want to get a raise or corner office at (as it were) you have to work towards the reward. Most would say well that would be the expansion and seeing as I have paid for it why is the content I paid for blocked off? Like many have stated it is lore they have in place. Ishgard is secluded. Opening only to those seen as allies. So seeing as how the jobs "trainers" are located there it only makes sense that you have to be able to get through the gates of judgment. And the only way to do that at the moment is to complete the storyline.
I won't lie and say that I don't feel some sense of regret for possible newer players that may have wanted to come to play Dark Knight, Machinist, or Astrologian. I can imagine it would be frustrating to find out (if you didn't know before hand) that you had to level to 50 and complete 2.0 storyline just to get that one job you were aching to play. But it would make no logical sense for someone level 30 to walk into Ishgard, a level 50+ zone, to get a job.
Ultimately there has to be something other than flying, larger areas, and other assorted new things in the expansion to draw people. Especially those who have been here since 1.0 and 2.0 beta forwards.
TL;DR Unhappy as some may be, it is the way it is. The only solution would be to put them in Coerthas and you would still have to be 30 to unlock them. No matter how it is done there will be a waiting period.