This is just the data structure so far; the codegen bits are still to come.

So we don't want/need to expose a way to get the data correctly typed based on the underlying array from ArrayBufferView?

Not yet; WebGL doesn't need it. Given DataViews, it's not quite clear what "correctly typed" would even mean in general for ArrayBufferView. Things that want to take some subset of ArrayBuferViews that happen to be actual typed arrays should be using overloads in the IDL, I would think.

And note that in extreme corner cases the callee does have the JSOject*.