Comment 2 for bug 394757

I have some reservations about silently ignore import failures of entire backends. I think I would prefer the backends themselves to do any 'tricks' they might want to do with respect to not importing modules that we consider to be optional.

The intent is to avoid making it easier to introduce problems that don't show up during development because code was not even imported.

But I definitely like the concept of listing backends and whether or not they "think" they are available, along with how to use them.