What’s this comically-proportioned W213 Mercedes-Benz E-Class? Must be a work-in-progress mash-up, then, and according to our spy photographer sources, this could be the development test mule for the next-generation Mercedes-Benz and Mercedes-AMG SL. It does strike us as a little peculiar that E-Class bodywork is used, even as a disguise, rather than the S-Class, which the roadster is closer to in hierarchy.

At present, the R231-generation SL has been around for nearly eight years, with the facelift arriving four years after. As the current generation approaches a decade of service, the time for an all-new SL could be ripe. The forthcoming SL will be closely related to the successor of the AMG GT, and both will be produced at AMG’s headquarters in Affalterbach, Germany, according to sources.

It’s early days for predicting the technical specifications of the next-generation SL, if indeed this is what the temporary oddity will turn out to be. Given its flagship roadster positioning, however, the next SL is likely to follow tradition in offering the latest in six- and eight-cylinder powerplants, namely the M256 and M176 inline-six and V8 engines, respectively. As a forthcoming model, any future AMG SL will be subject to the performance arm’s new AWD direction.

The SL’s historically long lifecycle also means that the COMAND infotainment setup – which has gradually been phased out elsewhere in the German automaker’s product line-up – has soldiered on with the latest iteration of the R231 roadster, the Grand Edition that debuted in February, and will also be a prime candidate for upgrading to the latest MBUX interface which has been incorporated into the likes of the GLE, GLC and GLC Coupe.

GALLERY: R231 Mercedes-Benz SL Grand Edition