People struggle to get their Bluetooth headphones to pair reliably with their phone, can you imagine the nightmare of simultaneously pairing with a phone, an excavator, and two bulldozers?
I think you would pair your headphones with some type of primary multiplexer that knows how to talk to the other gear and is probably centrally managed by the foreman. So your headphones in this model could see one device and thus you could use standard bluetooth headphones. I could see some type of Arduino or similar device acting as the multiplexer. Unsure if an arduino is capable enough but others here could probably chime in. That device could also handle the local communications. Maybe its a RasPi in a bright yellow case that goes on your tool belt with a DeWalt/Hilti/Bosch logo, whomever you partner with to fund this. Oh and a removable standard speed charging battery standardized to charge with the other tools.
Bluetooth is insufficiently reliable for this application.
What would be better?
Analog broadcast. Or digital, maybe, but still one-way broadcast.
Sound waves broadcast really well through air, and they come with localization information built in to the signal.
The problem we're trying to solve in the headphones is that sound waves are neutralized by the headphones.
I suppose that works for the headphones that have FM receivers. I use those today for playing mp3's in the vehicle since I only use older vehicles. Tricky part is workers close to each other having to coordinate frequencies but it's doable.