KDK isn't an answer anyway. It's a sandbox. It's restrictive.
And jailbreak (or, more precisely, rooting) would be done even in case of freely accessible KDK and official way of KDK app sideloading. Just look at Android ecosystem (hint: Android SDK is freely accessible and any user can install .apk without problems).
Here is an official letter about rejecting of KDK request (and no, they don't
apply mentioned strategy to firmware updates assembling):