That's a very good question and everyone seems to dance around the answer. Many people have published white papers, thesis, strategies, etc. on whether the current bluetooth hardware stack (CSR chipset) can even support stereo. Many companies have announced BT stereo headsets, but none that I'm aware of ever made it to market.

I do see some prototypes that seem to be progressing but they're using a totally different chip set and protocol stack design. They're more of a complete package than just a headset (e.g. an MP3 player that can connect via bluetooth to stereo headsets designed to work with the host unit).

A recent Bluetooth SIG newsletter has the head of Nokia talking of eSCO's (extended SCO, which translates to no SCO and all ASL) to overcome the "legacy design and outdated performance". Also, it's often mentioned that the current protocol is just way too "noisy". Much is discussed of a more efficient frequency-hopping to make for a more efficient WPAN and one that plays well with WiFi in the same frequency.

My feeling is that we'll end up with two protocol stacks. The existing which works very well for many uses and a more advanced stack to handle streaming audio and video. Much like "b" WiFi vs "g". "b" will never give you true bandwidth and performance for streaming video, but for most purposes it fits the bill.