Some precedents:~ As Florence noted, in 2007, Erik made a similar transition. (A bit contentious; there was a long internal-l thread).
And on Foundation-l.
~ In 2013, Ting stepped down from the Board to apply to the ED search; and addressed concerns at the time. (Discussion on this list)
Try this link. Though I couldn't find any replies to Ting on Wikimedia-l, maybe the real discussion happened elsewhere.
P.S.: With Mailman3, the Wikimedia-l archives are now fully
searchable through the web UI. You can even search across all
lists at once.