People are not bored of the B4 which is pretty much the same as its always been for 10-11 years. Many of the best tires for 2wd off road are older than that. Despite these things the class has been one of the most steady in RC since the very beginning.
The class has been buoyed by introductions of new chassis designs, most notably the TLR 22. This thing sure is neat but is much more of a niche vehicle which I think Durango is happy with. They're occupying the spot I would have expected a brand like X-ray to go after.