Right now the devs are mostly focusing on getting their next game going. That being said, they do plan to keep MageQuit updated in the future, though the updates will be less frequent as they focus on their new game.
Breet has mentioned in the past that they want to make sure the number of spells keeps the game approachable to new players. With 70 spells already, I'm not sure they'll add more as it could quickly get intimidating to newer players. They have been very open to adding new maps in the past though!
If you're willing there's a channel in the discord for ideas, and they're always looking there for things the community wants. If not, feel free to post ideas here and I can pass that along too =]