I will echo my desire to see a smaller size too. I have read quite a few good reviews on the larger displays. But 50" is too large for my room. I'd like to see a 40-45" size set too.
It doesn't look like they have any plans on doing so, at least yet.
The new A2000 and XBR2 series SXRD sets both seem to be limited to 50" and 60" models and those models are brand new. Strangely, they're still limiting even their new smaller rear-pro's to 3LCD 720p technology.
At the smaller sizes, RPTV horizontal resolution is held way below the 1920 across for 1080i/1080p because of the rib pitch (analogous to dot pitch of direct view CRT's) of the screen. Get up real close to any RPTV and you will see that the picture "breaks up into" thin uniform vertical stripes less than a millimeter apart but still probably fewer than 1000 across a 40 inch screen.
(Plasmas and direct view LCD panels also have dot pitches although LCD has achieved much finer dot pitches to date. Both of these technologies, unlike CRT and any RPTV, have 1:1 pixel match with the dot pitch giving better resolution for a given dot pitch.)