Nice idea. I had a real problem when I installed LEDs in my WW, I damn near had a seizure when multiball started and all the GI started to flash.

I eventually went with a solution of using a different product, the EnerGI Maestro, to control the things in a smoother fashion. I also had to modify the backbox wiring to separate out lights into two strings similar to what was done here, with the Whirlwind letters on one and the rest on another. After some custom cables to connect to this up, and bypassing the existing relays with some jumper plugs, it works reasonably well. The major downside is that this device only supports a single trigger line, rather than independent ones for each string. With Whirlwind, the upper playfield string is one trigger and the lower playfield and backbox main lights are another, so I lose some of the visual effects such as when one half of the playfield turns off and the other stays on, but it definitely got rid of the very fast flashing and strobing.

I like your approach in that you can decide how many to use, and also keep the independent flashing. I wonder if a centrally located solution in the backbox would work and keep the parts count down, rather than replacing individual relay boards?

Which is why if you do get this into production, I would likely back out the approach I am using and instead go with this.