I watched the segment. It was obvious that he only said "Yes. I will." in a desperate attempt to change the subject.
He'll sign when a flying pig brings him the pen.
I watched it too. The "Yes I will" was a throwaway line, uttered quickly and without any conviction, in an effort to bury the issue and move the conversation along to something else. He had been cornered by Russert and just blurted this out to get Russert off his back. The qualifications, stipulations, and evasions will come later, and we will not see the 180, ever.
Like I said I believe it when I see it