Just a thought, and I'm not certain if what I'm suggesting is a serous solution or a facetious one, but here goes:

A. Count all posts, including OMNI
B. At 10k posts, instead of becoming "Evangelist", the member's post count gets reset to Zero. At that point they can't access OMNI until they once again achieve 180 posts.

The 180 days will not be a requirement the second (or third...) time around, since they already have 180 days, unless they are less than that time from their original join date. (not likely, but possible). The 180 days will remain a requirement the first time around, of course.

This will have several effects. People who post massive amounts in OMNI will have to take a short break and catch their breath. People who love having high post counts will slow down after 8k and make every post count, and not post meaningless posts for a few weeks. People who say post count doesn't count will see a more even playing field. People who feel the lack of counting OMNI posts makes them second class citizens or devalues their contribs will no longer have to feel that way.

I don't post in OMNI, but I see it does fill a very interesting, valuable role. Where else on the 'net can you find such active debate from opposite viewpoints without one side driving the other away? (not on blogs, for example, they are very one sided). I'm concerned that, if the current shift causes dedicated OMNIvores to leave, that will diminish the unique place which it has become.