Err, yeah, so the fact that GeomPrimitive doesn’t actually create the index until it’s needed allows you to “work around” this hardware limitation–in OpenGL, for certain drivers, in certain rendering modes. But for the most part, you’re not supposed to do that. You can’t really go beyond 16-bit indexes on current-generation hardware (although some OpenGL drivers will automatically remap this for you). DirectX simply doesn’t allow it.
Really, you’re just not supposed to stuff more than 65536 vertices into a single GeomPrimitive. Even though it works in some limited cases, it’s not optimal. One day this will be supported transparently, especially when there is hardware that can handle it.
The CycleData bit, by the way, is just the standard way that Panda stores data in its classes to implement pipelining–different versions of an object for the different stages of the graphics pipeline visible in different threads (not yet fully implemented). For the most part, you can treat things within a CycleData object as if they are things within the class itself.
David