I think that is a very important point to consider. Once you start building your glass collection (Which you will despite any thought of you sticking with one lens. It's an unavoidable addiction) it's pretty hard to switch.
I originally chose Nikon because at the time, the D700 was the best camera for what I wanted to shoot. Now I'm on a D800 with a bit of a glass collection. My only regret is that all of our videography work is on Canons, so if I had just bit the bullet early and bought a Canon body, the access to lenses and equipment would be quadruple.
I'm still very happy with my choice. I love Nikons. Sorry I don't have any other help with the decision. I have never used any of the Sony cameras, but have heard nothing but good things lately on them. I will say this, when it comes to the upper echelon of cameras, 90% of us won't really get the most out of every inch, thus we'd all be just fine shooting on whatever platform. I'd say put both in your hands, play with them as much as you can and get the one that makes the most sense to you and with the way it feels in your hands.
