Mayhap some kind of class merge? Like a sniper/spy class? Has a revolver secondary and the ability to cloak and sap but also a sniper. I honestly think this would change the meta of TF2, having a class that can cover so many niche options but still they are ultimately niche.
The class would be balanced by having the shield and revolver slot be the same slot, and the user of the class has to fucking kill themselves that stupid sack of shit. Fuck you.