Currently a lot of callbacks passed to Mojo require a lot of base::Unretained(). It would be nice to think of patterns that reduce the prevalence of this; many times, the InterfacePtr / Binding is owned by |this|, so having to annotate each reply callback / connection error handler with a comment that this is safe because the corresponding Mojo construct is owned by |this| and won't invoke its callbacks after it goes out of scope, yadda yadda yadda, is a lot of wasted boilerplate.