Thank you for the provided feedback and the proposed workaround. Currently, we cannot officially claim that ICustomTypeProvider is supported by RadPropertyGrid out of the box. However, we will put this on the top of our priority list. Meanwhile, I have updated your Telerik points status by adding 1000 points in accordance to your report and your invested effort for finding a workaround. I will come back to you as soon as we are ready with this feature.
the Telerik team