While Slot 1 is loaded, Rig Button 1 is ready for a second click, but the other four Rig Buttons 2-5 are ready for first clicks to load Slots 2-5. If these would switch parameters within Slot 1, how would you reach the other four Slots?
The second click on Rig Button 1 does exactly what you describe "morph several parameters on one click", if Rig Button Morph is enabled. You can trigger Morphing via Rig Button or external momentary switches. Why do you need this functionality twice within one Rig?
I don't understand the concrete "business case". Sometimes I have the impression people don't make effective use of the capability to memorize 625 complete signal chains in Performance Mode. If the target is to cover all possible sound permutations with just one to three Rigs, we might run out of buttons and pedals.
So, please describe the scenario as concrete as possible for what you need a seperate (from Morphing) control of Delay Mix and Reverb Mix. And not from the perspective of how the feature should look like, but from the perspective of the need: "when this happens on stage I want to adjust Delay Mix and cannot use Morphing, because....". Based on this understanding we can consider the most effective approach to cover this need. Looper Volume is clear as this is not in scope of Morphing today.