If you do something like `GET /crashes/frequency/product/Firefox` I know the `frequency` part is used to find `get_frequency` in the Crashes class. But what's left of args in that case?

In principle, the comment is quite useless unless we do something about it. I think a good middle ground would be to do something like `import warnings; warnings.warn("Specifying parameters by URL path is deprecated and will be removed", DeprecationWarning)`