I personally think an espionage class with sappers or EMP blockers would be a terrible idea at this point in the game, and at any point really. Allow me to explain (rant incoming)
So in TF2, there are 9 classes, one of which builds Vending Machines, and the other one shanks people in da bum. The average size of a team on a pub is ~10, which means every team is statistically speaking going to have an engineer (not all teams have engineers, not enough people who play TF2 have common sense.) That means the spy will theoretically always have something to sap with his sapper.
Now lets take a look at dirty bomb. Right now, 8 mercs (if I’m not mistaken.) Only one can build a building, and he can only build one, a sentry. The sentry already has really low health, and can be broken in one strong knife (alt-fire). If an espionage class were to be added right now, his sappers would be effective against one building. Not very good. Not only that, but only three mercs can be chosen by one person at any time, and teams don’t go above 8 aside. The chance of one team having Bushwacker, and the other having espionage class are pretty high, but the usefulness of the espionage classes’ sapper would still be really low. Unless more mercs are added to the game with buildings, then a sapper would still be useless.
BUT THEN, if more mercs are added, the statistical chance of an espionage class being on one team, and the other team having a decent number of engineers is quite low, as more mercs are added, and the three merc pool doesn’t increase.
So yea, no sappers for Dirty Bomb I’m afraid, we’ll just have to stick with Skyhammer spam. If you find any weak points in my argument, feel free to argue back.