Disregarding the very fine points other people have come up with, it shouldn't be .bitcoin. It would be .btc, no one would use a top-level domain 7 characters long.
I think you'll feel very differently in a couple of years. Do we only go to .com sites because that's all there really was before?
I think there are many good points above. I actually think registering .bitcoin would be a colosal waste of money. I was just curious how others felt. But, .whatevers will become ubiquitous.
You also make a great point, and it's certainly possible. I was a little hyperbolic saying "no one".
However, I still believe that sticking with shorter top-levels would be a good idea simply for ease of typing in the URL. In a best case scenario IMO, .com would just be .c or .co, although at this stage in the Internet I'm sure most of the people versed in the Internet have muscle memory to type ".com" in at lightning speed.