I also believe that the +2 threshold should initially be a tentative one, subject to later review by the RSB. The ultimate goal, IMHO, should be an improvement to the overall happiness of the developer community.
I can envision a cultural divide where a simple +2 threshold leads to a nearly 50/50 split of the community - with the result being increasingly hardened battle-lines and all the negative results that implies. The answer, however, likely won't be known until a point in time weeks if not months after this experiment is put to the test. Therefore a previously agreed upon ability to change the threshold allows the rules to be tweaked in order to best achieve the goal.