Long term, who knows. But we would like to be able to do date calculations a couple of years into future.
On the fairly safe assumption that you don't care about being off by a few seconds, leap seconds aren't a factor there. Assuming one leap second every month (!), your computed date two years out will be off by less than half a minute. No one will ever even notice; the entities that consume dates in calendar format -- people -- aren't capable of meeting time tolerances that tight.
If you need to coordinate something down to the millisecond, calendar dates aren't for you.
If this coordination needs to happen > 6 months in the future, then UTC is the wrong time standard to use. Use TAI.