How does Vuforia Fusion fall back to ARCore for plane detection?

I'm currently developing an Android and iOS app which will rely on the use of ARCore and ARKit for plane detection. I was planning to use Vuforia for both the handy cross-platform capabilities and to possibly support a bigger number of devices either with "pure" Ground Plane (when ARCore/Kit are not available) or 3DOF capabilities in the "worst case", with Rotational Tracking.

Problem is that it doesn't look like Vuforia Fusion is able to detect ARCore availability. I'm testing my application on an Asus Zenfone AR: it is "formally" a device not supported by Vuforia Ground Plane, although with the release of ARCore 1.0 it also got included in the list of devices where the ARCore apk can be installed. What I would expect would be Ground Plane to fall back to the ARCore SDK but this is not the case: 6DOF capabilities don't work at all when using Vuforia (needless to say that they do when using the "native" ARCore library in Unity).

My point is: I would gladly use Vuforia as a "one for all" solution, but how can I guarantee that future ARCore supporting devices will be able to leverage on Ground Plane? At the moment it looks like I will need to update my app everytime Vuforia adds new devices with a newer release and this doesn't look very feasible.
Or am I doing something wrong?

Thanks!