I have absolutely no knowledge or involvement with any matter involving MathOverflow governance, including the initiative described in this question. I'm commenting based on my experience with policymaking more generally, both as a creator and subject of policy.
My opinion, in short, is: transparency at the early stages of the policymaking process is in nobody's best interests. The basic reason is that the process works best when many ideas are considered but the bad ones are killed off as quickly and secretly as possible.
Suppose it is discovered, for example, that a number of MO users who post about differential geometry a lot are toxic and driving away users that MO wants to attract. (This example is purely fictional.) Suppose somebody proposes to deal with this problem by banning the differential geometry tag from MO, almost certainly a bad idea.
Scenario 1: public debate. Yes, there would be good arguments about how it's silly to ban an entire field of mathematics due to a few bad actors. But there would probably also be bad arguments made by people who don't like differential geometry, and the toxic users themselves would probably make a scene. A big mess would ensue, and the whole episode would risk driving people away from the site.
Scenario 2: private debate. Even if the proposal had one or two passionate advocates, the argument that banning a major field of mathematical research will help attract more MO users is untenable and would be killed quietly, assuming a suitably informed and diverse group of participants are invited to the discussion.
Obviously scenario 2 is better. Out of the box thinking is good, but some ideas should be quietly put back in the box.
Of course, the extreme lack of transparency also carries risks - I wouldn't want MO to unveil a bunch of controversial new policies without providing users with a chance to ask questions and propose changes. Though the MO board has every right to take such an action if deemed appropriate. If the site had significant financial incentives to aggressively drive user growth or appease a corporate investor then I might be concerned, but so far as I am aware everyone is properly incentivized to create a healthy community for mathematicians.