50 megapixel full frame!.
Does Sony have a 50mp DSLR, nope.
Does Nikon have a 50mp DSLR, nope.
Once again Canon is way ahead and creams the competiton

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Errrhh actually yes Fred. Sony Exmor 46-50mp full frame sensor is about to be released in a couple of Sony bodies and a Nikon body (rumour is within a few weeks). This will be an Exmor sensor with its superior Dynamic Range and possibly better high ISO performance (Canon are quite good there). The main advantage would be the better Dynamic Range where Sony Exmor sensors do well in low ISO low noise (ie. little noise in the shadows).
50mp for a nightscape camera could be quite interesting though. You really only need the ISO6400 performance so if it does match 5D3 or slightly better for noise it could make some nice night images.
A widefield Milky Way shot with a 100mm lens could be pretty spectacular.
The sample Canon 5DSr shots are impressive.
Greg.