Yeah, we're aware of it. Here's where most racetracks are with this system: At any given racetrack, you can expect a corner worker will need to be in a flag station to monitor the corners, radio calls to race control, and wave flags. In the case of many racetracks, (A) there is frequently only one flagger in a station and (B) the workload is already significant doing just those three things.
Adding a fourth item (some kind of electronic trigger for the in-car flagging system) increases the high workload even more. When we tested one system at a race, the feedback was that the in-car system was occasionally (though not frequently) at odds with the flag being shown (or not shown) at the corner station. For several reasons, if we did use an in-car system, I think Lemons' inclination would be to have a station still showing physical flags for the sake of redundancy so a one-for-one switch of physical flags for total reliance on the in-car system is extremely unlikely. So Problem 1 is finding enough corner workers to manage the additional workload.
Additionally, before we would implement such a system and make you pay money on it (and possibly a subscription, as is the model for some systems), it would have to work at every racetrack we go to and every racetrack we potentially go to. That means flaggers who can handle it and track infrastructure that can also support it. That's Problem 2 because I can tell you that is not currently feasible.
There is a secondary (tertiary?) issue of setting expectations for novice drivers that perhaps is unfounded, but perhaps isn't. When a new person gets into a Lemons car, we want them to be looking up and aware of the situations ahead of them. Eyes scanning and picking up flag stations is good behavior that we want to impart on new people. I'm not totally sold on having a buzzer or light or however the notification comes right in the driver's eye, taking a new driver's eye down instead of looking up.
If you're a regular poster on this board, you probably could handle it in stride, but when someone is on the track for the first time, the last thing I would want if for them to suddenly be looking down or right or 18 inches from their face instead of up at what is ahead. If the in-car system is also at odds with a physical flag, then what the hell happens for a new driver? I'd say 99/100 probably treat it like a yellow, but there are enough n00bs in Lemons that one "WATCH THIS LOSER" dude could potentially make a huge issue.
I could opine onto why I think people want this to be a good idea, but I'll spare you.
Everything Bagel, 24 Hours of Lemons