One risk about making arguments public is that those who originated the arguments stand to lose more face if they are shown to be incorrect publicly than privately. (I'm sure all four of the individuals you refer to care more about having accurate beliefs than preserving face, but I thought it was worth pointing out.) Not that this problem is not exclusive to the wiki proposal; it also applies to just writing more papers.

I think it makes sense in general to present one's conclusions as tentative even if one holds them with high confidence, just to guard against this sort of thing. Redundancy is good. Why not have two mechanisms to guard against any face-saving instinct?