I fully agree, we should have low-level classes that have OpenGL in their names. We should just not advertise to users that these low-level classes exist (don’t use in any examples and minimize their usage in tests) because we know that in a few years we will have alternative implementations.
It is about the same as with vtkActor / vtkOpenGLActor. Only advanced users should instantiate vtkOpenGLActor explicitly, everyone else should just use vtkActor and rely on VTK factory (or any other suitable mechanism) to instantiate the best implementation.
We should add the new implementation-agnostic classes at the same time we rename the existing classes. This allows users to switch to the final class names in one step instead of renaming classes in tests, examples, user code now and again in 1-2 years. Yes, it may require 1-2 extra days of work for a VTK developer now, but it may save an hour or more for hundreds of VTK-based projects.