Blue Mage is supposed to add a completely different gameplay. For its limitations with endgame content, It'll be able to do things that no other class can. The fact that SE has prevented it from doing endgame content means that they can go as overboard as they want, and try new things without worrying about limiting what Blue Mage can or can't do.

So yes, I believe that Blue Mage will be its own experience and its own challenge, something interesting to try out. You can still do endgame with many other classes-- 2 more coming in 5.0! If you have enjoyed endgame so far without Blue, nothing is preventing you from continuing to enjoy it.