It would be a downgrade in my opinion because you would loose your point source.  Using one for bass and one for mids would require two non-matching drivers each with different phase angles and different speeds and of course a crossover which will introduce it's own issues.  

Don't get me wrong, it will all work, in fact it could be a kick ass hi-fi speaker, but not the goose-bump generator it is now, which comes from it's simplicity.

Also, I have been listening to whizzer cones and ribbons side by side for about 15 years on an almost daily basis and the difference isn't obvious. What the whizzer may lack in speed compared to the ribbon, the ribbon lacks because it's not in the correct location, requires a crossover, and has a different phase angle... so it's almost a wash.

Steve