I am very impressed with the Nikon D750. Yes, I believe this is a camera that could trigger a person to switch platforms. The thought ran through my mind for sure.
Positives: FF, Built-In WiFi, Dual SD card slots, Good AF, 24+ MP Sensor, 6.3fps
Negatives: 1/4000 shutter speed limit, Weather Sealing?
Neutral: Articulating Screen, Built-In Flash, ISO
I'm not about to rush out and sell my Canon gear and switch, but I agree (at least on paper) the D750 does look like it might be a great camera for many people/purposes (not saying it will suit everyone, of course). I basically agree with your list of pros and cons, although I'd rate the articulating screen and the built-in flash as negatives if they compromise weather-sealing or durability (but do they?). I also have a question mark over the ergonomics. Looking at the screenshots of the D750, I am unconvinced about the ergonomics, but of course you really need to shoot with one before deciding about that.
I have to say I feel like Nikon has had a habit of making products with great specs but which (as far as I can tell from what I've read) in actual use often are no better than, and sometimes worse than, comparable offerings from Canon and others. (I'm not talking about the SoNikon sensors though - but there has been enough written about them already.) I guess we need to see how the D750 actually performs, but if the D750 lives up to its specs, I'd be pretty happy about it if I shot Nikon.
It will be interesting to see what the next round of full-frame cameras from Canon will bring.
Edit - just saw some posts above wondering about the D750's buffer. That's definitely something to find out more about!