Nobody will a join a union just to strike ( a.k.a pull the apps) however making collective to better negotiate with someone with lot of control over your revenue (salary) is not inherently a dumb idea.
App Store developers are sprinkled all over the world, so not too much is consistent between them. Getting enough of these varied people to collectively pause their income, and allow their competitors to flourish, long enough for Apple to even notice/care, is probably much harder. I think it would be even harder to present the applications failure in a way that an average consumer would sympathize with or even understand.
You only need really apps with say 10-50M downloads to join together, most of them know each other and many of them are made by rival companies who have an interest in keeping Apple in check.
Indie developers could of course be invited to join such action, but apart from PR and other aspects they won't move the needle either way with Apple.