It's been done before, although only once by the factory. Many have outfitted aftermarket hardtop kits to their Mazda MX-5 Miatas, but an OEM option is generally preferred. Not so long ago, Mazda indicated that at some point down the road a coupe variant of the newly redesigned MX-5 will launch. Consider it a gift to the purists out there. It may even have a fastback roof design. Remember the old BMW Z3 coupe? That had a shooting brake design, but we doubt Mazda will go that route.
Whatever design is ultimately chosen, we're anxious to see the coupe come to fruition. Rendering artist Theophilus Chin has come up with a few images showing how a MX-5 coupe could end up. It's actually a pretty conservative take by just adding a fixed roof and more heavily sloped rear glass. And you know what, this may be more than good enough. It's a nice blend of shooting brake, fastback, and simple coupe; sort of the best of everything. And it could end up being the Subaru BRZ and Scion FR-S's worst nightmare.