Exactly. Discontinuing leap seconds is a 99.999999% compatible change. I've tried to build systems using TAI they break down because: At some point you have

Exactly. Discontinuing leap seconds is a 99.999999% compatible change. I've tried to build systems using TAI they break down because: At some point you have to interact with something that doesn't use TAI and that fully reintroduces all the leap second issues, and because a lot of third party software has leap second handling, so the wheels fall off when you update some component and its embedded list of historical leapseconds now changes its behavior. Similarly, sometimes UTC time is all that's available and without the leap second data you can't back them out to get TAI. And with leapsmear the challenges of backing out to TAI have increase substantially.