That's the sad part. If there's one thing that the open-source community produces an abundance of, it's definitely text editors, but music players are a close second.

Previously, we've had XMMS as an open-source project that supported WinAmp skins.
And right now, perfectly actively maintained, there is QMMP.

I'd bet money that the code quality of QMMP is a lot higher than that of WinAmp. So, if anyone wanted an open-source WinAmp, it was there all along.