I came up with this as a solution to the fact that most/some weapons aren't worth charging because they either take too long, have a poor charge attack, or you keep getting hit before you can do them.
Basically, it works like this- you charge your weapon, but fire it off before it's fully charged. And it doesn't do the Charge attack of the weapon, but something else entirely.
Guns would probably benefit/make the most sense with this idea, I guess it can be used for one special bomb/bomb line (or to give a buff to some otherwise totally useless bombs), and you could probably inject some usefulness into the Spur line by granting it an Alt-fire mode that involves knocking enemies away with a gust of wind produced by revving the motor on the sword retardedly fast.
I'm actually a fan of the idea of having a pistol whip feature with guns, but I guess thats what shield block is for :P
well, I think the original intent behind the guns was actually to be sort of "mega man-esk" which I love. if you don't fully charge the shot, than it's not a charged shot, simple. on the other hand, and to go along with what your saying, "half" charged shots in "Mega man x" actually were more powerful than a normal shot, but, it took precisely half of the time of the full charge to get there, so you couldn't charge "half a sec" and expect to get the green, slightly stronger shot off.
meh, if you add this, it would mostly just complicate a very simple system. I would rather see a larger variety of weapons, than an "alt-fire" mode for each one. plus alt-fire is normally a button in and of it's own, not a "charge" feature of every weapon. that said, not every weapon deserves an "alt-fire".
plus, if a gun had an alt fire, they'd need to go and add that into the guns description, and if they wanted to do that for any "pre-existing" gun, that would be a LOT of work, a lot more than it would probably be worth.
interesting idea, but I don't think it works for spiral knights, SK is just too simple to add anything that would complicate the weapons to this degree, or that could require the use of an additional button.