It is a good practice to create a 12 month waiting period before board members of non-profits can become a staff member/paid contractor/consultant.

A few people mentioned that their own orgs or committees have norms or policies around this (Chris, Philip, Tito); could you describe specifics that are in place now around the movement?

It's interesting that you mention norms and policies... Wikimedia UK's policy on this (1) for instance states 

"During the period of trusteeship, and for six months after leaving the board, no trustee may without the consent of the board accept any employed or remunerated consultancy position with, nor may offer remunerated consultancy services to:

This is rather more in-depth than the WMF's policy, at least so far as I can see. Though not so in-depth as the previous version of the policy, which also required seeking the approval of the UK's charity regulator.

Even so, the policy could permit this kind of situation if the Board decided to approve the arrangement. However, no sensible Board would do so, because of exactly the kind of reaction that you see in this thread.