i think a great and probably easy to realize idea for the blend mode filter would be to have a level / percentage so you can adjust how much this layer adds to the final output. For example when you have layers in an image editing software you can adjust the opacity with a percentage level.
Probably not going to happen. Another suggestion was to add Opacity to every video filter. Sigh. Maybe there should not be separate filters, and there is simply one giant filter that turns things on and off under the hood. Yeah, not going to happen either.