I think I understand what you are communicating but then again I may be way off base.
First of all, naming an engine after the version of the graphics renderer it uses is a mistake in my opinion. They probably made this decision because, at the time, there weren't really any other sandbox editors out there that could claim x10. However, now it just illustrates how outdated the graphics rendering is at this point.
All that said, directX is a feature set. There is almost nothing being done in x10 or x11 that can't be done in an x9 based engine. If you have a top-notch graphics programmer, they can add the same functionality and feature sets.
I know this to be true, as several of the folks in my lab have implemented features from x10 and x11 into our OGRE3D (x9) engine.
I think people get too hung up on the version of a graphics renderer. The important question is...does the engine have the feature sets you are looking for to make your game.
My thoughts anyway. But then again, I may have completely missed your point.
