So the thinking behind this is you have the switch centers actually pressing into the Sorbothane. You're then making contact with the key where it bottoms out as well as the entire PCB. Since most sound is generated where the switch bottoms out, you're damping this exact spot before those high frequencies go anywhere else. The PCB being mounted to the bottom insert was also so that the sound generated by it gets transmitted down and away instead of through the mounting surface.
When I get the Proto I'm going to do a sound test with some holy pandas vs a standard 60% aluminum case. Likely have enough data by this weekend to get it made.
Full disclosure, I'm not interested in buying this keeb, I only use ortho, but I honestly don't think this will work. I'm not saying it to be mean or anything, I'm taking a guess that your prototype will run at $300 or so excluding the sorbo, please consider this before spending a ton on a prototype.
If your try tapping a integrated plate, you will have a ping sound, almost like strings or a drum skin.
I have a niu mini that I tried to dampen with bottom foam (mind you it was not sorbo, but a very low shore, high density foam) and that did not work.
What I ended up doing was putting a 3mm brass plate in between the integrated plate and the PCB, suspended between two layers of compressed 1mm foam, and then some foam at the bottom under the PCB as well.
This did not remove all the ping (but a lot), so I eventually settled for silent switches, which have internal damping as well.
See, unless you're using holy pandas (or some kailh switches) the sliders will hit, and they hit closer to where the switch meets the plate. HP (and some kailh switches) have a longer plunger that hits the bottom where you'd have sorbo. This is not normal, it's an exception.
Maybe you could save some money and order a smaller version as a first prototype, and figure out if the mounting and damping works first. Or get a niu top and putting a ton of sorbo underneath to see if it helps.