I await your Book with great interest HTBWC !
I also like very much the Hypothesis you outline in your O.P, I would so very much like for it to be affirmed and to be accepted, at least by Scholars, J.W's and other Fundies will proceed regardless, they don't go much for Scholarship, Facts or Evidence.
It is though, as you outline it above, hardly a credible Hypothesis that other Scholars will agree with, but maybe you will go in to greater depth on this more in your Book ? make a stronger case ? As I said, I do desire it to be spot on, but also desire its acceptance by those who matter in the field of N.T Studies.
It is amazing how things have moved on in the last few decades, the consensus among N.T Scholars is as you say in your O.P, I think many of them err on the side of caution, out of fear of what other Big Guns in the world of N.T Studies may say, but at least things have moved on from the early 20th Century, where a quite silly view of the time of writing for the Synoptics etc was the consensus.
Maybe you will give the old boys, ( and girls) of N.T Studies, a nudge further in the right direction, with your Book !