I can easily see an endgame, done with existing maps.
*spoiler notes in hypothetical endgame, don't read without having done ToAU missions to date*
In their drive to activate Alexander, Al Zahbi engineers a control and power scheme using the artificial AC's + the schematics locked in Aphamau's automaton and attempts to bring the iron giant online.
(Gee, the death star plans are in the cute little robot- Star Wars gets another cute nod. Go SE.

)
They succeed- too well. Alexander locks out all non-recognized persons and proceeds on a countdown to go fully active- and amok, the additional power burning out any restraints the original construct had. If the system isn't fully shut down, Alexander will reform and reduce first the Empire to a glassy pit, then everything else in order to "defend" the world from the Dark Rider. Of course, with the extra power, Alexander's subsystems- the chariots and gears- are in overdrive as well.
And by recognized, we mean "you've got the key from Nyzul Level 100". Good luck, heroes. If you fail, there will be nobody left to remember you by. Get in there and hit all the failsafes to bring Alexander offline once again. Since it's gone mad, the key will get you in, but you'll have to fight your way into the AC's and disable them, and quite possibly the core if tinkering with the power supplies causes Alexander to initiate a self-destruct.
*spoilerness over*
How's that for an endgame? Since Alexander = Remnants + Nyzul Isle, we already have every map for endgame in the .dats. Fully instanceable, even. A sort of FFIV Tower of Bab-il sequence.