I favor design by contract so I can properly type-hint method parameters.  A framework should be written in a way I can safely extend the crap out of.  This is the exact use case of interfaces.

Universal constructors make the code harder to read.  I see this as a sign that inheritance is being used way too much.  Compose people, compose!

The registry pattern is not any better than a singleton.  They both have global scope.

I do like that there are so many ways to inject dependencies.  The MVC framework is also pretty nice.