This does raise the question; will Knoebels do something to fill the space? Some have mentioned that the front area of Knoebels, where 1001 Nachts and the Italian Trapeze (the 2 most mentioned contenders for this mystery ride removal), may be a prime spot for their next major attraction. However, it's most likely that this ride will either not be replaced in general, or replaced at a later time than 2020.
As for Knoebels' next coaster project, I could see the revival of the wooden wild mouse - a compact and very unique ride that would be right at home among Knoebels' other old-school thrills. The argument can be made that a wooden wild mouse could be too similar to Black Diamond, but in my opinion the latter is an indoor, watered-down version of a wild mouse that would be seen as a family-friendly version to the wooden wild mouse, if built.
Whatever comes of this, I'm certainly hooked - Knoebels is my favorite park, so I like to keep up on whatever they're up to.