Well, if making blue mage a real job isn't possible, what I'd like to see happen is for other limited jobs to be added so that blue mages could team up with them and do old content together. Like you'd have a blue mage, a beastmaster, and a puppetmaster all working together to steamroll old content. :v It'd add a sort of sideways progression to the game so that there is more stuff to do at endgame than just raid and grind out better gear. So by excluding these jobs from the traditional endgame, you're kind of creating a new endgame at the same time?
I get I'm probably in the minority here though since I'm not big on raiding at all.