[AdmirableAdmiral]

If low classes/ races are becoming an issue because of deck size, you could separate those cards, shuffle and deal one to each player at the beginning of the game, and then shuffle them into the full deck and deal out the hands.

Another way to combat it would be to make Class/ Race cards playable on anyone. I've been thinking about making this a house rule. For example, when losing combat, a player could say "Whoever helps me becomes a thief."
(I've even considered making a class on a blank card with some power like that. Think Career Assignment Personnel from Futurama)

Problems I see are when people already have a class (simply say they must accept the card being played on them, or else it is immediately discarded). That also solves the Cultist problem, since there is a card specifically designed to make one a cultist. The Epic C.A.P can forcefully switch the class of another Epic Munchkin.

I thought I saw somewhere a rule about posting card ideas here to prevent loss of intellectual property, but I hereby waive my right to the idea and anyone may use it.