I've spent a lot of time finding objects in the sky to high accuracy with astronomical algorithms. The first step is always converting from UTC to TAI. See Astronomical Algorithms by Jean Meeus if you don't believe me.
Your noon example works for a single longitude in a time zone and the time between subsequent noons on two different days will only be exactly 24 hours 4 times a year. It seems unnecessarily complex to push annual leap second updates to preserve something like as obscure as these 4 events for the 24 time zones exactly on the line of longitude to the accuracy of a second.
See the Wikipedia on abolishing leap seconds, "that the drift of about one minute every 60–90 years could be compared to the 16-minute annual variation between true solar time and mean solar time, the one hour offset by use of daylight time, and the several-hours offset in certain geographically extra-large time zones"