Winamp 3 beta does not have this as a plugin anymore, but rather "built-in". In addition there is now a Alpha of Winamp3 available for linux.. maybe some code from there could be re-used with permission? or am i just waaaaaaaaaaay off.. It also allows to set the time of the crossfader.
And i agree. if its a feature you can turn on and off. then anyone could decide on their own whether it sounds good for their tastes or not.