From a current article from DirtBike Magazine: "Yamaha’s bombshell was the announcement of an off-road two-stroke for 2016. The new YZ250X is an off-road (meaning, not motocross) version of the YZ250, much like a two-stroke version of the FX. It’s in a slightly different state of tune than the YZ motocrosser, but it has off-road stuff like an 18-inch rear wheel, a wide-ratio transmission, a more tucked-in pipe and a kickstand. If you were around in 1997 you remember the last time this happened. Back then Yamaha had a 250cc two-stroke off-road bike called the WR250. Since those days, the EPA and the California Air Resources Board got involved. The government started asking if a bike was intended for closed-course competition or not. If the manufacturer said “not,” then the bike had to pass emission tests.
The result was the end of trail-oriented two-strokes, at least as far as Japanese bikes go. Europeans, on the other hand, kept right on importing them. It’s taken this long for the rank-and-file engineers and test riders at Yamaha to convince upper management that they can do the same thing. A bike can be designed for off-road racing and be imported as a closed course competition bike; the two aren’t mutually exclusive.
Design-wise, the YZ250X is somewhat conservative. It isn’t an electric-start 300 as some pundits speculated. Yamaha was already risking a lot without the massive retooling that an all-new motor would have required. But, if the X is successful, it could lead to more of its kind."