This is odd for a couple of reasons. For one, now that the Hellcat has a wider version, it seems strange that Dodge would be working on a car with more power, but with less tire to make use of it. For reference, this prototype is wearing 275-mm tires front and rear, whereas the normal Demon has 315s at each corner, and the Hellcat Widebody has 305s. And it seems that this isn't just an old Demon prototype, since the wheels and tires are narrow enough that they fit properly under the normal fenders.
This car is also unusual because Dodge said the Demon is finished after this year. Once the 3,000 units are sold, there won't be any others. But obviously the company is still playing around with the engine and some kind of application of it.
Of course, perhaps this isn't a Demon at all. Maybe the next-generation Hellcat will use a version of the Demon's engine, and it will be offered in both normal Hellcat and Widebody body styles. If this is the case, it will be interesting to see if Dodge continues to offer the engine with the full-blown 840-horsepower tune that requires 100-octane race gas. Since the car is certified for federal emissions with that tune, it would make sense to offer it, but it may become an option as opposed to part of the whole Demon package. It will be interesting to see what happens with Dodge's powerful monsters.