This could eventually open up other markets for SpaceX. A communication network with that density would be able to offer a better resolution than GPS and sets up SpaceX to be a key backbone service provider for autonomous flying vehicles in any form. Be that personal transports/air taxis or courier drones.
Whilst not the intended market initially and might be some design considerations that prevent that level of branching out. But certainly, something to ponder down the line.
Offering a GPS-like service would require totally different hardware. Each GPS satellite has 4 atomic clocks. The StarLink satellites will basically be optical routers and their timekeeping needs can probably be handled by a cheap clock and NTP from the ground.
Could have multiple clock sources on earth that produce the clock signals for the satellites. So a satellite could get an accurate time if it locked onto a few ground based sources.
Just with that volume and density of satellites, kinda begs some lateral thinking.
Whilst not the intended market initially and might be some design considerations that prevent that level of branching out. But certainly, something to ponder down the line.