The Swedish astrophotographer Göran Strand published the first review of the Nikon D810A camera on his blog. The ISO comparison between the D810, D800E and D3s clearly shows the advantages of the D810A (click for larger view):
Positive
- Very good high ISO performance
- More sensitive in H-alpha
- No need for a computer when doing astrophotography
- Boosted live view
- Long exposure M* mode
- Electronic Front-Curtain Shutter
- Good battery life
Negative
- No tiltable LCD
- No backlit camera buttons
- Boosted live view can be a bit noisy
- Higher sensitivity to red light could cause some problem for general daylight photography
The Nikon D810A camera is still not available in the US. According to Amazon, shipping will start on June 8th, 2015.