It possibly could be done in real-time using Bluetooth but I doubt it would be reliable and remember that higher end cameras might be writing out images at maybe 6+ frames/second. Alternatively you can make a point of recording a track on your phone (which tends to be hard on the battery life) and then syncing them up later. But, as someone who has done this, it's a pain in the neck.

Geotagging on my X-T3 with the Camera remote Android app is very reliable to be honest. And you don't have to query the phone at the same rate as you're taking pictures, it's perfectly sane to assume the same location for 5-10 seconds during a burst.

Fair enough. Though I'm not sure I'm convinced that, today, you're not just better off putting a GPS receiver in the camera. GPS is a bit hard on battery life but with the bigger batteries in these cameras, I'm not sure that's much of an issue. (And of course you can turn it off.)

Depends. MILCs are generally pretty hard on battery and keeping a constant GPS lock would exacerbate their generally poor "active standby" (camera turned on with the viewfinder or LCD active) battery life. On the other hand, my smartphone, using both GPS and augmented network location services can instead very quickly acquire a lock when needed with minimal battery usage only when needed. And it also has a way larger battery, and the system is generally more optimized.

If I'm using a standalone camera, I don't want to be fiddling with other devices just to get geotagging working.