This would be a total gamechanger and completely change my workflow: the ability of applying filters such as Camera Raw or a simple Gaussian Blur to an adjustment layer would save so much time- talking about this given the new Clarity/Remove fog/Noise/Temperature-tint adjustment layers update that's been announced on Instagram. It's something the competence (Affinity Photo) does have and it's amazing. As for how it'd work- it would probably have to be just a "Smart Filter Adjustment Layer" which applies to all the layers below (something similar to After Effects)- same thing for previsualization of the effect, all the layers below. Live changes would be amazing. This would probably consume a lot of cpu so, in that case, it could be added as something optional to activate in preferences if you have a good PC/Mac. Would LOVE to see this happen.