Looks like a pair of solid all-rounders, albeit that the price of the D5 makes it somewhat irrelevant (Working sports/photojournalists may be able to justify it, but not many consumers I'd hazard a guess). That AF system sounds impressive though, and I love the idea of CF/SD cards becoming user choice (I hate SD cards, so much less direct/secure when inserting).
I reckon the D810 replacement will be an impressive beast as it's likely to mix the D500 feature set with a FX sensor (significantly less FPS most likely, but who cares!) - and the Sony sensors Nikon are using at the moment are just killing it - they've introduced properly broad dynamic range to D-SLRs.
It's a pretty timely announcement by Nikon too - Canon would want to have something phenomenal coming in the 5D Mk.IV because their range is starting to look very, very tired.