The CBA rationale for the lack of engagement between the Pats and Brady makes some sense. Both sides, and particularly the Pats, need to know how much cap room they have.
That said, if both sides were motivated to get something done or to at least explore the possibility, I would think that some preliminary conversations, including with respect to duration could take place. I would also think that they could both make some assumptions about where the CBA will end up and agree to finalize once things have clarified. On the other hand, I do appreciate that "hypothetical negotiations" are not easy, to say the least. I just wonder if the CBA is as complete of an answer as it appears.
Somewhat unrelated: I have no idea how credible Jeff Darlington is and whether to ascribe anything to his report. I had a similar reaction to Seth Wickersham and his article a few years ago. If Darlington is just about attention gathering, well he achieved that. And I guess he can back away later by saying that Brady must have had a change of heart. But that's a pretty big limb he's out on. Knowing more about his credibility would be interesting.