I cornered Sean Pringle in a dark alley and had him explain it.
To summarize, there have been slave issues when UCA collation was being deployed on fr.wp and thus more deployments were held off just in case. However, wikis that are not in large.dblist should be good to go at any time.
Wikis that are in large.dblist should have somebody monitoring the job with a kill stick and DBA tools ready, but are probably also good to go thanks to Aaron's patch https://gerrit.wikimedia.org/r/#/c/151027/.
I'm going to try cornering some more people in near future to get this unstuck. :D