I’ll be honest, I didn’t expect that video on that muscle sensor to be so engaging 
I find the concept of a WILD device intriguing because I think every dream device I’ve seen has been developed for DILDs.
However, I’m not sure how what you describe will necessarily help with WILD.
Mind you, I’m no expert on the WILD technique. I’ve been a lucid dreamer for over a decade now and I can probably count my WILDs on both hands , I probably average about one a year and it’s almost always an accident in the middle of the night. I found that it’s just not my technique.
Back to the concept you proposed, I’m wondering how an external stimulus that correlates to your muscles relaxing would help with WILD.
My experience and understanding of the technique is that you actually have to let your body fall asleep and also let your mind fall asleep to some extent. I find the technique to be tricky because it requires a specific balance of mind kinda awake and body asleep. In my experience, the consciousness it requires is more like a meditative awareness opposed to active thinking.
In that way, I wonder if a physically stimulating device may be counterproductive to WILD? Because your body needs to fall asleep and bringing in waking life input may just keep you awake and leave you with a poor night’s sleep.
But on the contrary, I wonder if you could develop a technique with the device similar to the goal of the WILD variant FILD. But…even with that in mind, it would be easier and more comfortable to just do the FILD technique with the fingers, opposed to trying to program a device connected to your muscles for some kind of stimulation.
If you were able to provide a little mental stimulation with the device as your muscles relaxed (like a sound as you mention)…it might work to remind you that you’re falling asleep???Maybe?? Big maybe.
I feel like a guided sleep meditation or a recording on a timer could accomplish the same goal, though.
Maybe there’s someone in the forum that has
A bit more insight and experience with WILD that can chime in here.
If WILD is a technique you struggle with, I might instead suggest trying for DILDs? As a whole they tend to be less disruptive to sleep and I find it much easier.
In any case, I don’t think devices are necessarily the best investment you can make in your dreaming adventure. They’re pretty interesting, but your time and energy is probably better spent keeping up with a dream journal, getting to know your dreams, and adopting a lucid mindset (questioning reality and letting go of the conviction that you could know that you’re not dreaming).