I really like the way in the private space the user installed apps are separated from the system apps. Unlikely I'm sure but would be nice for AOSP give that at option for the owner profile.
Also, it'd be ideal I'd you could install Play Store in the Private Space then push apps to the owner profile, that way you could benefit from the Play Store security for app installs and updates but then lock the private space when not needed so google play isn't running at all times.
Probably not possible, but sounds like it'd be a decent feature.