My original question was wondering if these had some syntactic sugar or more mature incarnations in another module already done (like Perl 6 "but" feature).

No, there isn't any sugar. I think there are two reasons for that, 1) doing custom infix operators are pretty much impossible, 2) people don't mind the Role->meta->apply syntax that much (and 3, applying roles to instances is not all that commonly used a feature).

But, I'm also supposing that I'm not breaking new ground in wanting an extension mechanism for a more complex case (not a single class, but functionality is broken up into smaller classes) and other people may have approached it already.

Well, there is also MooseX::Object::Pluggable, but I think perhaps people are still exploring the possible features/complex-insanity that Moose and runtime-roles open up, so you probably have a lot of funky stuff out in the DarkPAN that has yet to reach the CPAN. Honestly, the Moose community on IRC is pretty active, I really think you would benefit from getting involved there.