That’s an interesting suggestion, but I think it’s important to also consider how you plan to use the “time” field.
If you just want that field to represent the exact, literal UTC time that the photo was taken, regardless of where in the world you are, then your solution works perfectly. All of your photos can always be perfectly sorted chronologically to when you took them.
On the other hand, if you ever find yourself searching for photos taken at a certain local time of day, across different time zones, then you might find yourself struggling with mapping the location tags to timezones to build the the query you need.
For my purposes, I think it’s sufficient for photos within a given roll/shoot to be sorted chronologically and be roughly accurate to the local time. Even if the timezone is off, my bigger peeve is when there’s a difficult to correct delta between two cameras used in the same project.
In my ideal world, my cameras would have a built-in GNSS sensor and automatically set the time from the satellite signals (optionally recording either the local time or UTC). Many smartphones almost work this way already.
That’s why we (should) have time zone information (or an offset from UTC, they are not the same: time zones can change).
Shouldn’t that be something you can check and correct beforehand (for me, “project” implies some sort of communication between participants. And if it’s a one-person project, well…)
Yes and no. Sometimes you can sync cameras to a common time source ahead of time. Sometimes you can’t.
One trick I use is to run a stop watch on my phone and then photograph the screen with each camera so that I can calculate the offset and do batch adjustments with exiftool. Sometimes this can even work after-the-fact, as long as you still have access to all the cameras and the clock drift isn’t too bad.
It would just be nice to not need to do this extra manual step, since we have free and accurate time sources beaming down the current time at us at all times. It would cost the camera companies a few pennies per camera to add a GPS sensor and use it to periodically sync the internal clock, and since it knows your position it could include UTC offset and timezone information at the same time.