Ultimate alien should have been Ben's symbiote arc
The ultimatrix is one of the most wasted ideeas in the show, and i think turning it into Ben's "dark suit" would not only have made it actually relevant to the show in a way that the normal omnitrix could not, but would also justify Ben not using it anymore at the end of the show. Imagine if Ben got addicted to using the ultimates, like with feedback. The ultimates would slowly develope personalities of their own, kinda like how rath has his own personality, over time they would start influencing Ben, making him more agressive which would tie up pretty well with the aggregor and ultimate kevin arcs. This would culminate in Ben loosing control of the ultimates, i imagine a scene of Ben transformed into ult echo echo trying to kill a random villain, gwen screaming "Ben!" and ult echo echo responding "Ben isn't here anymore". They would eventually manage to make Ben come to his senses long enough to turn back into himself, then they would ask azmuth to permanently lock the ultimate transformations, making sure this never happens again. Then when albedo get the ability to transform into ultimates his mind would be overwelmed by all thier personalities, imagine the scene at the end of the nighmare episod but he's surounded by ultimates instead.