These suggestions may be more work than usual, but you could try to include a template version of every 'category' of skill you know is possible in the demos so we could look at them and alter them up to use in our games as a base to start from.
Another is to add the ability for characters to change character sprites based on a skill state, like, they get special attack animations rn as an optional thing, but unless there's some janky workaround I'm unaware of, there's no inbuilt way to make characters change appearance if they have a specific state, could be useful for stuff like a powered up state.
Another idea for an ability usecase would be a 'swap' state, so the caster puts a swap state on someone, if one of these two characters die, the other swaps to their spot instantly.
Or
Special teleportation, where a character can be moved to somewhere selected on the map somehow instead of a random place.
I dunno if this stuff is already included in the extensions or not however.