There are plans for an SVG based skinning system, codenamed Maybel. The skinning system is still experimental at this point though, and has not been released into the stable builds. There are no plans to support Winamp3/5 "Modern" skins directly however. There exists a library that is in theory capable to load those skins (at least partially so far), called libWAL, but since the scripting core of Winamp3/5 skins is kept closed source by AOL, it would not be possible to realize a fully working skin loader without significant reverse engineering work.
Instead, the developers decided to define a new skin format, which will also improve on a few shortcomings of the WAL skin format, such as allowing for vectorized objects (in form of SVGs), and vectorized/splined paths along which e.g. sliders can move (think of a wave-shaped volume slider, for example), just to name a few features.
BMPx was rewritten from scratch, borrowing only a handful of utility functions from the BMP (and indirectly XMMS) codebase. Following the move to C++, even these functions have been rewritten to make better use of the language.
While early releases of BMPx retained the WinAmp look through a reimplemented skinning engine which made use of GTK+ widgets more extensively, the developers decided to shelve it in favor of a more integrated, iTunes-inspired look that popular players such as Amarok have adopted.
As of December 2007, the project's original domain "beep-media-player.org" expired due to a communication problem. Since then the website content has been moved to the new domain bmpx.backtrace.info