Python does a decent job with multiple inheritance,
Eh, so does C++.
The only time C++ really has trouble is if A and B share the names of methods/variables. And the reason they will have trouble is that there is no solvable way to not have trouble. Not for a computer. Not for a programmer.
Although, I don't see how you can possibly go wrong, if you can write to the module that contains A creating an interface A implements, and changing the code that the module uses to use said interface.. There's no difference for backwards compatibility. (Unless you don't believe in namespaces, and have to worry about truely unique names everywhere.)
"""Here there be dragons, beware"""
See, that's not something that is easy to search for in code reviews. Because, there is no validation that I did not write: *** Off the edge of the world: Sea Serpents Around ***
And if you cannot trust other programmers to use fucking interfaces, you cannot trust them to use the right magic strings.