This will sound crazy and totally wrong. But you might find it interesting, and if nothing more, you might also get a laugh out of it. I would not want one.
Here's what I experienced when I was commuting up and down the Seattle I-5 corridor. The first year I was doing my commute, I would use engine braking, but I'd also try to give some warning to the person following me by lightly touching the brake. I noticed a couple things. Drivers still tailgated me. It was like they realized they would get some warning if I slowed down, and so they took advantage of that. I also noticed my brake pads wore down to nothing in about 15,000 miles instead of the 30,000 miles that was normal for that bike.
After about a year and that first set of brake pads, I did something by accident and noticed a change. I had been following the advice in the Advanced Motorcycle Safety Course to keep 3-4 seconds following distance. Engine compression braking is very easy like that. (BTW, this is all riding in the HOV lane.) But for some reason, I didn't use my brake lever to activate the brake light. The person behind me had dropped back to about a 4-6 second following distance. I liked that!
So I started watching what happened with other drivers, and found they all did the same thing. No longer did I have anyone tailgating me. I put about 130,000 commuting miles on the next several years, and it always worked. If they were tailgating initially, after a couple times of slowing down, they dropped back and never got close again. It was like how you treat a vehicle in front of you that you realize had no working brake lights. What do you do? You drop way back. First, you realize you have to watch to see if the vehicle is slowing down...and not with the extra warning brake lights give you. And second, if you're lucky, someone else will move into the open space, and they can deal with it and now you can relax.
I think a really bright brake light is wonderful. But I really don't want to give the driver behind me a reason to think he/she/it can tailgate me and have any extra warning with something that lights up to say I'm slowing down.
One last thing... You have mirrors for a reason. When you try this, don't do it blindly. Watch to see what happens. And be ready to respond if they don't notice you slowing down.
One more last thing.
The first reaction a lot of riders have is that you can't ride with a 3-4 second following distance. I've had others who didn't think it would work try it...and come back later and say it worked for them.
Chris