I'd like to see more dual-typed moves. I don't mind whether they're signature moves or not, although I guess limited distribution might help (unsure if my tune will change about that "limited distribution" idea). If any do turn up to be signature moves, they had better be one of the most competitively viable moves in that particular Pokemon's movepool; otherwise, I feel like the implementation would seem like a wasted opportunity.
The existent move Muddy Water seems like it would work well as a Water-type/Ground-type move, in my opinion, as it mixes the substances of soil and water...
Also, hopefully in a future generation, the move menus have enough space to somehow display both types that a dual-typed move utilizes (for example, the "move type" icon of the move Flying Press would feature both the Fighting-type icon and the Flying-type icon, as opposed to just being listed solely with a Fighting-type icon, with the move description being relegated to explain its dual-typed nature).
On a side-note, if I recall correctly, there was a rumored dual-type Electric/Grass move (in one of the more major "circulated XY rumor lists") alongside Flying Press during XY's pre-release era. However, while Flying Press turned out to actually exist, currently the other "Electric/Grass" move does not (either being outright fake, or being an unknown downloadable content/event-exclusive move). Does anyone remember the name and/or concept of the rumored "Electric/Grass" move, if it does/did exist..?