I’ve just read someone else’s idea in another thread and it’s also good: Idea for follower cap! FUNCOM PLEASE READ!
The author of the idea proposes a Barracks system, where you would be able to place a new structure called Barracks. It would work similar to an Animal Pen, holding thralls you’re not using. You could take the followers out of it and deploy them and send them back to barracks with a command in the radial menu. If you couple that idea with the thrall limit, it would work well for everyone: total cap would still be in place, but you could easily change the deployment of your thralls. Getting purged at base X? Go to base Y, send all the thralls there to their barracks, go back to base X, deploy thralls from barracks there, fight the purge, then put everything back to the way it was.
I still think a density cap would be less complicated for players and devs both, but barracks system sounds like an interesting idea.