Basic gray bag
It kind of makes sense. It's a neutral color/design that would more or less go with any Kirby made in the last 25 years or so and it would allow them to stock only two outer bags, the latest Avalir bag and the generic replacement. Besides, Kirby already has done this with replacement parts for pre-G models so one might even see it as an inevitable move.
That said, the generic gray bag would definitely look better with some machines than others. In my opinion, it would look best on machines that already have a gray color scheme (e.g., G3, G4, Ultimate G and Sentria). But I can see where some G5 and Gsix owners could be disappointed to send their machine in for a factory rebuild and have come back without the distinctive burgundy or black bag. That said, I personally have no objection to the look of the gray Ultimate G bag assembly I have on my G5, but the burgundy flecks in the fabric do help tie the look together.