I know, but I don't know what iOS webkit does and doesn't allow. Injecting code and responding to events in a way that makes the most important webextension APIs work _sounds_ like it should be possible (though it would take lots of work).

Sad to hear there's no such feature on iOS. At least Android gets uBlock Origin in the stable channels. Hopefully this will change when Apple will eventually be forced to permit other browsers into the iOS app store.