The current car-player software, even internal builds, always flushes the bit reservoir between tracks even for consecutive tracks from the same album. A future version will not flush the decoder in that case, which should allow true gapless playback

VERY interesting idea. But...

I have tried two different gapless playback plugins for WinAmp, one of which behaved as you just spec'd (don't flush the reservoir).

My hand-trimmed files that sounded good with the "flushing" version, had a burst of static at the transition points with the "non-flushing" version.

Okay, I'll admit that my hand-trimming technique is totally nonstandard, and deserves to get broken by a hypothetical future release of the software. But...

The thing you're talking about implementing sounds like the only time it would work perfectly is when the user has created a single large MP3 and then hand-split it at frame boundaries. It wouldn't help hand-trimmers like me, and it wouldn't help those who encoded their CDs normally. It also wouldn't improve upon the LAME--nogap files because (if I understand it correctly), the reason LAME's method works is because it makes sure the bit reservior is unused at track boundaries.