Which would make it only slightly less useful than the much simpler, more readily available, and mature technologies that have been available for decades.
Except that unlike the typical RF bug this can't be swept for - no transmitter to catch per se - Which puts it in the parabolic or laser mic class oh shit category.
Remember back when it was "safe" to just shut off your cell phone..?
Actually it can be swept for. Modern bug sweeping technology already includes the capability to find the solid state circuit which would be embedding the audio in the light. That's in no small part because there are already plenty of tricks for making RF bugs resistant to RF sweeps. Bugs can transmit in microbursts, rotating frequencies, or simply close enough to normal RF frequencies like TV or radio to be indistinguishable from normal background noise. Even relatively simple spread spectrum broadcasts are nearly detection resistant.
And as you point out, remotely accessing every day devices is already a reality. Considering most people have one or more electronic devices with transmit capabilities on their person most of the time that's a much more efficient, and obviously scarier, way to eavesdrop.
What scares me the most isn't the technology that's available but rather how little thought most people give to intentionally transmitting sensitive data here, there, and everywhere. That makes finding and exploiting vulnerabilities easier by an order of magnitude which ultimately impacts even those of use who are obsessively careful.
The question isn't whether you're paranoid. It's whether you're paranoid enough - and very few people are. If you've got nothing to hide you haven't given it enough thought.