I think that might be a bad idea, because when thugs say "hand over your phone" and you hand them a brand new phone that you have apparently never used, you're going to get wrench-based cryptanalysis. You need to be able to hand them the keys to a realistic environment that looks like it's being used. Thugs wanna see recent timestamps.
Ideally, we need to have some casual, boring (but constantly-touched!) environment that can launch encrypted environments, but somehow not have anything that references those environments.
The biggest problem I see is storage allocation. We need to be able to plausibly deny the existence of something, but also keep it from being overwritten by not-denied environments. How do you hide "don't write to these blocks, because something else uses them"?
Some might suggest hiding in plain sight with steganography, but at some point thugs will notice that everyone they suspect, just happens to have an unnecessarily-large gigaphoto. ;-)
Having alt environments that are detectable, but can be quickly destroyed the way you suggest, might be a decent compromise as long as it keeps an innocent and recently-used one around as cover. You enter the oh-fuck PIN, and it logs you into the innocent host environment but then it immediately deletes its encrypted guests, leaving you with a truly innocent machine as far as anyone can tell. And then you just really hope you can enter that duress code (or you can trick thugs into entering it) before they image your storage.