For the ending, everyone wears identical suits (the one Sally wears during Cabaret, but with a shirt on) except for Cliff and Herr Schultz who wear their regular costumes. The whole cast stand on the revolve facing forward (as if they're standing in a line) as it spins around the Emcee on a raised platform in the center (also wearing a matching suit). None of the Kit Kat Club dancers nor the Emcee have any makeup on.
The theme of this production is definitely the infiltration of the last refuge and this is the final form of that. The refuge has been infiltrated and those who were once some of the most unique in Berlin are now just more suits in an almost endless line of suits. Cliff and Herr Schultz are singled out, Cliff by his choosing and Herr Schultz despite his. They don't need concentration camp uniforms or anything else to single them out.
I found the whole thing extremely effective.
Side notes: that progression is very well shown. We see the Emcee in and out of this suit throughout the show and the ensemble in it during the second act. There is also a big moment when Sally puts hers on before Cabaret. But, this is the first time that Fraulein Schneider (and I think Ernst) don one and the first time we see everyone together with them on. The scene is also very similar to the way they stage the first Tomorrow Belongs to Me except that they do that one with the ensemble placing identical dolls on the revolve. With hindsight, it's the showing the way some Berliners have already lost their uniqueness but that the people of Kit Kat Club haven't yet. By the end of the show we are left with only two people not part of the assimilation.