Its not a leap once a century thing, it's a rejigger the timezones by an hour every four to five thousand years. (either define new zones one hour over or redefine existing ones)

We already rejigger the time zones from time to time, so thats already handled. It's still a source of issues, sure, but it's once source instead of two.

The timezone rejiggering could also be set hundreds of years in advance... rather than the very short notice we get for leap seconds.