In my original comment, when I wrote timezone, I actually didn’t really mean one of many known civil timezones (because it’s not), but I meant “timezone string configuration in Linux that will then give TAI time, ie stop adjusting it with timezones, daylight savings, or leap seconds”.
I hadn’t heard of the concept of timescale.
Personally i think item (3) is worthless for computer (as opposed to human facing) timekeeping.
Your explanation is very educational, thank you.
That said, you say it’s simple to get TAI, but that’s within a programming language. What we need is a way to explicitly specify the meaning of a time (timezone but also timescale, I’m learning), and that that interpretation is stored together with the timestamp.
I still don’t understand why a TZ=TAI would be so unreasonable or hard to implement as a shorthand for this desire..
I’m thinking particularly of it being attractive for logfiles and other long term data with time info in it.