I very much think Blue Mage should remain a limited job, as even as a limited job it can do just about all the content if they are given the ability to reach max level. And limited doesn't mean a lower max level, or at least doesn't have to. The way it's set up is that limited means they just can't use the Duty Finder.
And I do hope they spend a good amount of time working on Blue Mage once Shadowbringers hits so they can get it to 80. They've stated they have a good amount of new spells planned out for it and have said that the first proper patch after Shadowbringers release, meaning 5.05 or 5.1, they will update BLU to reach 60.