so we're all definitely missing leap seconds?
If you work with TAI you wouldn’t be using typical Date types anyway, just a raw counter. Now, raw counter data is not being send over the web. NTP (that’s what all our devices are using) is operating using monotonic time with no notion of Leap Seconds - insted on days with leap seconds NTP servers slow down to accomodate them.
And if you have local access to an atomic clock it would be just another device access. Nodejs, serial port addon - and bam, you have TAI data in JavaScript.