And the fact that you need to create a wrapper means that some programmers won't bother to do it, or won't know they need to do it. The default case handling timezones correctly will reduce potential errors.

Time zone transition changes happen all the time. Once you start storing datetimes in the future, you're in a bit of a precarious position here. Moreover, this is a standardized interchange format that other libraries will know how to read/write. (It's relatively newly standardized, but has been used in practice among other datetime libraries.)

I think you also glossed over some of my other points. How do you write your serialization code using Chrono? Does it work with both chrono-tz and tzfile?

The point is almost never about "it is literally impossible to accomplish task foo," but rather, it matters how it's approach and how easy it is to do. And if you have to rely on your users having very specific domain knowledge about this, it's likely there will be errors. As my design docs state, I didn't only make Jiff to offer more functionality. I also made it because I felt like the APIs could be better. That's a very subjective valuation, and I find arguments of the type, "well I can just use the old library in this way as long as I hold it right and it actually works just fine" to be missing the forest for the trees.