Plus you can group together people in the same area and/or sort positions as integers and store only the deltas between them, so you can probably get down to 2-3 bytes per person.
And you can get dozens of models of smartphone with 16GB of RAM right now. So there might be a gap there but it's a very small gap. The phone of tomorrow will have the RAM.
Edit: Thinking about it more, with 2^33 people and 2^47 locations the average delta would be 2^14, and it's pretty easy to guarantee that fits into 2 bytes per person. And with a more accurate world population count you'd free up at least a gigabyte for your phone to actually operate with.
Judging by that, you need a negligible increase in the number of locations you can represent to handle everywhere stable and off the ground someone could be. Much less than one bit per person.
If you want to deal with people currently in airplanes then you could give them an extra couple bytes. It's less than a million people so it won't affect your total storage at all.
And in places you care (multi-floor buildings) you aren't getting GPS signal inside anyway...
