> This is the other part: if associate membership is a thing then won't half of the EU start thinking that's their future?

Presumably by "half of the EU" you mean (sometimes) euro-sceptic states like Hungary or Poland? Well, these are not in EU because some illuminati/lizard people tricked them into joining and now won't allow them to leave, like some of their politicians would like you to believe, but because they enjoy billions of subsidies per year.