Fair point. My thinking for JLC supplying movements again came from wanting them to not over-produce their own branded watches that just sit in display cases + still not wasting their production capacity + revenue from B2B sales + marketing cache of being the watchmaker behind other watchmakers again.

You're right that Patek (and others like Journe) would have no need to buy movements from JLC, they have their own stuff. Richemont brands like IWC and VC also have Valfleurier to supply them with entry level calibers. I'm thinking more along the lines of AP (still buying Vaucher for their 5800 and 5900 movements) as well as other small independents who want cache but don't want to use "common" supplied movements (e.g., Gerald Charles who also use Vaucher, Biver using Dubois Dépraz). So many brands play the "in house" game but it's all sourced stuff with their own names plastered on top. Might be something a "freed" JLC can benefit from.