Add item:on_command_pressed() and item:on_command_released() events
For certain types of items (eg, Gust Jar in Minish Cap) it would be useful to define equipment item events for when the command is held and released separately. This way, holding the command could activate the item, and releasing it could make it finish.
There's also a relevant thread here: http://forum.solarus-games.org/index.php/topic,999
P.S. Let me know if you'd rather not have feature requests here, I'm having lots of ideas as I explore the engine.