I haven't played Malifaux in a while but I remember thinking that identities were starting to fuzz a little around the edges. It wouldn't be the first game where distinctive disadvantages that define a character or faction eventually have answers to fill in the gaps.
Every new wave creates potential balance issues as the model pool grows. The design space shrinks because you're always stuck with all of the previously defined actions and the potential for unintended interactions grow. It must be very difficult to add extra models without eclipsing some of the older ones.
Obviously it wouldn't work for a table top game, but I find it interesting how trading card games rotate sets. There you only have a limited pool to worry about in terms of balance and the design space is continually refreshed. The rotated cards can at least be played in other formats. The alternative, which I really dislike, is nerfing characters that are too popular, the way games like Hearthstone have done in the past to avoid having to rotate them.
If and when Malifaux does define a new version, I will be very interested. I'd much prefer that "Gremlins" keep the name though, especially since they escaped "Outcasts" way back when.