Moi Benjamin! I just found out that Tommi decided to orphan mpg123, and poked through the related thread in wnpp. If you choose to withdraw your ITA, please drop me a note--I'd consider adopting it as well. Michael, the upstream, and me are working at the same university, and therefore meet from time to time. This might help working out some of the issues on the package.
As for the licensing issues, Michael explicitly permit distribution of patches+original source, so tools like yada might provide an elegant way of solving the issue. Now the really interesting part, of course, is the library part of mpg123, which has been LGPL'ed in the meantime. It will have to go into its own source package though. Best regards, Daniel.