History people, History... Xing disappeared, was absorbed by Real... FHG went to work with AAC, Thompson has the mp3 format now, and they made mp3pro. So no, don't expect much more from this format. There is real pressure coming from other formats, like AAC, Ogg Vorbis, etc against MP3. Sorry but i think you came like 5 years late to see any real competition taking place, and the format is almost nearing full optimization. There can't be any major improvements in quality because of the limits the format itself imposes, another reason why there is not much sense for the mentioned companies to keep working too much with it.
However your comment would be just perfect for Ogg Vorbis, despite the format being complete, there is only a single encoder which is not getting tweaked or improved enough, and no alternatives... But at least the format has lots of room for improvement, and things with AAC are heating (many encoders there

) I think you just need to dump this old legacy format, or be happy with lame APS.