Phil Askey has published his review of Nikon's latest DSLR on DP Review.
The D50 has a couple of features that seems advantageous for underwater photography. Compared with the D70 it has an improved viewfinder and also a improved image processing algorithm 'to clip less and have a softer roll off to highlight" (like the D2x), which promises to offer improved handling of sunbursts.
Read Phil's review here:
http://www.dpreview.com/reviews/nikond50/
What is less clear is whether any housing manufacturers will offer housings for this camera. Afterall, designing and building another housing for a new model has large start up costs. Rather like the EOS 350D - maybe most housing manufacturers will concentrate on other models - arguing if you want to shoot a Nikon underwater you should choose a D70.
Digideep.com does not have any housings listed for this camera at the moment.
Alex