Chameleon is supposed to be both skinning and adapting technology. The core of it very advanced and simple skinning system, other part will be "detection" system that detects actual look&feel and adjusts U++ skin according to it.
It will definetly be a hit if it lets the user to choose between different custom skins and system or desktop look.
You know, I have been saying that OSX should be the next major dev task that should be completed, but the more I think about, I am changing my mind. I think the chameleon should be the next major dev task that should be finished after the BGAR business is done. I'm guessing there will be some low-level adjustments needed in core code to make this possible. Best to do the chameleon first as it will be a big hit, but while doing chameleon always have in back of your mind x-platform compatibility so you don't have to make major changes while porting to OSX and wince.