Yeah, my original assumption was that it was going to be the default. The reason I suggested a config var was that it seemed like an implementation detail that people should only be encouraged to change if they are experiencing issues. Giving it a bit more thought, however, this is a bit silly; it does require people to write their vertex shaders differently, so this is definitely something that should be explicitly specified.
With that in mind, it seems more appropriate to have it as parameter like you suggested. However, it might be even a bit more elegant to place it in the renderQuadInto and renderSceneInto calls, since different passes can use different shaders and each shader may assume a particular geometry.
I’m a little surprised that you feel so strongly about such a trivial thing, and I’m certainly not trying to push my own design standards or dissuade you from contributing. Either way, FilterManager is not my code, and I also think there are major flaws in its design. I intend to see it replaced altogether by a new system, one that would certainly make use of an oversized triangle by default, and one that provided a default vertex shader so that the developer wouldn’t have to write their shaders differently depending on what geometry is being used.