The problem with ! is that it's a shifted character, so it's not a good choice for something which you use many times a day. An unshifted character would be better. E.g. comma: ,w for wikipedia
It would be more efficient. If it was vim or emacs, you could rebind. I think it should be easy enough for ddg to make the special character customizable as set by a cookie.
From the perspective of someone who uses bangs daily, it doesn't doesn't make a difference in terms of UX
, is a marketing fail over ! though. (apologies to Yahoo)