An expression that returns the last key pressed on the keyboard as a string and a condition that checks for a key pressed based on that string. That would allow for customizable controls.
This is a high priority item, I feel. It's a standard of PC gaming, and especially for accessibility and disabled people's sake. Sure there's already the keycode plugin but it conflicts with Ashley's keyboard plugin.
I don't think many software developers are aware of the importance of customizable controls, as Clickteam and Construct Classic didn't have this support either (although Ashley has been getting a little bit better with the gamepad plugin at least).
Developing a game for a specific set of keys/gamepad is pretty much the worst thing you can do to a proffesional game, every person likes the controls a different way. Input is such an important part of the experience, and if you mess it up your game is going to be so much worse.