Yamaha updated the R6 last year which I think complies with the Euro4 thing, not sure that the other big 3 manufacturers have a new 600 Euro4 bike in the system, another point of linked info is that the 2019 Moto2 supplied / control engine will be a Triumph 765cc triple unit but at the same time Triumph have axed the Daytona from manufacture because the older 675 motor didn't meet Euro4 .. Honda have supplied the previous motors since Moto2 started so i'm guessing they don't see any future in 600's.