I'm​ had an idea for BLU not long ago I thought was pretty clever. Whether it's a DPS or tank, all of it's skills need to be universal. This is not even just a matter of certain people being "lazy" but also unintentionally missing out. That'd be a ton more work for gains that wouldn't put you above other Job. So, my idea was skill glamour. That is to say, all the skills will serve the same function, but you could "learn" a completely same functioning skill from some rando monster.

Example. A class quest gives you an AoE. Let's say it's Aqua Lung/Breath. Well, let's say you're out adventuring and slay some form of Malboro (Just killing it seems the smartest implementation IMO), and boom, you can now use Bad Breath, but only in place of Aqua Lung/Breath. This could apply for many other skill. Spider Web/Stone Gaze for slowing enemies down. Level ??? Death/Holy for an LB. It'd take a lot of work, and would honestly just be a vanity project for SE at that point, but who wouldn't love the job?

As for role, I'd say melee DPS, but with strong utility makes the most sense. Blu has always been about bringing the pain first, with very few, but very powerful​ utility skills (White Wind and Mighty Guard being prime examples).

Also, an aside here (If we do go tank), maybe if the story goes to Garlean, the BLU is a BLUe Knight. They mimic/capture/steal the powers of base monsters to replicate magic power since they can't use it naturally. It also gives us an excuse to have Micro Missile.