Had the same idea ...
Funny, just 1 hour ago I had the same idea (producing a nice-looking flush microSD adapter), so I started researching, found the "cut" solutions, found the Nifty MiniDrive project, and while I was reading the kickstarter page the "Updates" counter jumped from 1 to 2 and the third model (MiniDrive Retina) was announced ... I feel so live!
@makemineadouble:
If you are still following this thread, I have a suggestion. I think it was a nice feature, that the "normal" MiniDrive (now MiniDrive Air) would fit all Macs. Now with the Retina's slot being deeper, this versatility is lost.
But: what if you just slightly retool the aluminum front of the MiniDrive, making it either thinner or just edge some recesses out, so it would slide all the way into a MacBook Pro Retina? Sure, in addition to the rounded ends not fitting perfectly it would also not be flush any more. But at least it would be usable.
Another possibility would require even more retooling but would gain you flexibility even for unforeseeable future Apple products:
Make the aluminum front a separate slide-on part!
That way you could deliver multiple fronts or replacement fronts, or even a front-abo. (Provided, of course, that the actual reader part is expensive enough, that separating it would still be cheaper than simply adding it to every front you sell.)
Congratulations anyway! It's always good to see, how a nice idea can become a new business.