I would think so, but between Yoshida having said the balance team doesn't want to do 2 new jobs for an expansion because it's too much work combined with what we got with Heavensward (MCH and AST are a little too similar to other classes, with the latter built to mimick the two existing healers instead of aiming to do its own thing), I'm not exactly brimming with confidence. I more expect them to stick to existing systems and go from there.
The way dungeon runs go wouldn't really accommodate spell learning, but my point was that dungeon mobs seem to have more in the way of abilities with effects that could work for BLU. Another example is the fact that overworld Vultures don't have a knockback built into Wing Cutter, whereas Vultures in dungeons do (at least as of the last time I had anything to do with Vultures). So if you wanted BLU to learn Wing Cutter to have access to a knockback ability, you'd either have to change overworld Vultures so that their Wing Cutter has the knockback, force the BLU to learn it in a dungeon, or implement an alternative that bends the rules.Well, I don't really see a problem with learning something from the Lost City of Amdapor, if it comes to that, but if they want it available on a wider scale, they'd just include more mobs in the list of enemies you can learn it from. It's not that different from your own suggestion here about adding more mobs to the list of ones that can boost a spell to its full power. The main difference being I'd only include mobs at a level appropriate to when the skill should be learned. (I just can't see boosting the power of a level 50 skill by killing a few level 1 beetles.)