I have no idea what the mod tools and such are like on Lemmy, so I don’t know how feasible it is, but I feel like a good way to do it would be to enforce tagging posts, and once we hit a certain threshold of users using that tag the relevant community gets reopened
Making up numbers on the fly, but maybe something like after 100 different users have made posts with a certain tag and at least 10 of them have made at least 5 posts the relevant community gets reopened, and the main cooking community makes a stickied post and makes some automod comments or something advertising that it’s back open.
A lot of online communities get a lot of their content from a handful of power-users, so making sure that you have a handful of people who are repeatedly making relevant content I think is just as important as making sure you have bulk people who may only contribute occasionally, which is why I included having some users who have made multiple posts
Also when that critical mass is reached, some strategic timing for when to reopen them may be a good idea. Might get some extra buzz and activity to kick things off by reopening BBQ a couple weeks before memorial day when people are getting ready for summer cookouts and ask culinary around November as people are starting to plan for thanksgiving and Christmas