Reverse Teleconvertor?

Hi, just wondering if such a thing is possible.

Here's the idea: an optical attachment for use with 1.6x crop bodies and EF mount lenses, which would effectively function as a reverse teleconvertor. The attachment would compress the field of view provided by EF mount lenses so the field of view provided with the attachment would match the field of view provided by the lens when used on a full frame body.

Beyond the wider field of view, I would assume other advantages would include an improvement in light gathering by about a stop and a third, along with improved bokeh. Of course, more glass is also likely to reduce IQ, but I think the benefits would make the hit to IQ worth it.

Thoughts, comments, concerns? Why doesn't Canon make one of these?