This can be far cheaper than tactile pavement and so more widely deployed, more easily updated as the environment changes, and present different warnings to people with different needs ... like people with limited mobility ("warning 5 inch step down in 3 feet") or the unimpaired ("please do not run in this corridor").
With sufficiently accurate location data and ubiquitous networking, the transmitter isn't needed at all. Apps could curate warnings and other location specific info, and you could subscribe to the ones that are relevant to you. If location tech isn't up to the sub-meter resolution, the embedded transmitters could be used to just send their own exact location. Then you feed that to the app to return warnings, etc.
The etc. could include hyper-local ads, making the system self funding.
Especially for people with disabilities the world is not a hospitable place. I can't see how a 'modern' version if something as simple as tactile pavement would be any better for the disabled.
There are, for example, people who are both visually impaired and hearing impaired that are capable of guiding themselves around by cane, in these instances tactile pavement is something that I think your 'phone in hand' solution just doesn't work. Additionally, not everyone owns smart phones--even today.
I'm not saying your points are invalid but they're definitely skewed in favor of technology and perhaps a limited understanding of ADA requirements.
Yikes. Why do public goods always need to have ads to be self-sufficient?
> This can be far cheaper than tactile pavement and so more widely deployed […].
The cost of deploying low power transmitters, developing and certifying new systems (not everyone carry a smartphone) or mobile apps to receive the signal, educating impaired people across the world to use them, then regularly maintaining the electronics across a city will hardly be cheaper than passive tactile paving.