The MVC Stereo High profile used in 3D Blu-rays was designed to be backward compatible with existing dual stream decoders. It was specifically created for this purpose and differs from the more generic profiles. This is why the H.264 spec was updated late last year. The buffers still need to be compatible but it gives some hope for an upgrade path. The HDMI transmitter probably doesn't care too much since it doesn't buffer anything, and the bandwidth is well within version 1.3.