I wont. I doubt that many serious astrophotographers will for various reasons.
The main reason for using a DSLR in this application is low (relative) cost for the quality, which obviously doesn't go with full frame sensors. Most people will buy a low cost one, and then modify it either themselves or via existing services. The only niche this might fill is for someone going for bigger and bright objects, at gobbling 36MP at a time could be really nice.
As I understand it, the D810A may still have some minor advantages in that I understand it can boost live view levels over standard (could be very useful), plus has built in support for longer exposure times (less useful). Thom Hogan has questioned if these may be added to standard models later by firmware updates, which then negates the advantage.
Really serious astrophotographers including Bob and Greg use dedicated sensors made for the job. They're not cheap, but are built to deliver the lowest noise possible from both design and cooling. As good as the Sony/Nikon sensors are for normal use, they're not optimised in this way. They of course can still provide nice results when used well.
Canon DSLRs: 7D2, 7D1, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 85/1.8, 135/2+SF, 70-300L, 100-400L, 100L, MP-E 65, EF-S 10-18, 15-85
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 50/1.4A, 150 macro, 120-300 f/2.8 OS
Compacts: Sony HX9V, Fuji X100.