I woyld suggest quadratic blending modes as a way to increase flexibility of Krita brushing and blending. If you were to blend 2 different perpendicular gradients, there would be a quadratic form. Reflect and glow would increase Krita interchangability potential, and aforementioned things. a is layer 1, and b is layer 2. More info about quadratic blending modes here - http://www.pegtop.net/delphi/articles/blendmodes/quadratic.htm
I finally created those blending modes. I am now on the testing phase, so if it works out, I'll release the differentials.
They are now part of Krita 4.2 beta. So, this can be closed.