That's actually a good idea in the short term (i.e. less than one century). The length of the day (LOD) is thought to be linearly increasing in the long term th

That's actually a good idea in the short term (i.e. less than one century). The length of the day (LOD) is thought to be linearly increasing in the long term though, so ΔT, the cumulative difference between past SI days and actual LOD, should be quadratically increasing and a delayed leap second adjustment would be too slow to catch up at some point in the future. Yet another possibility is to put any possible kind of leap second at the beginning of the year. The only requirement set by past CGPMs is that dUTC = UT1 - UTC should be in [-0.9, +0.9] seconds, so we can always put a positive leap second when dUTC is in [-0.9, -0.1]s and a negative leap second when dUTC is in [+0.1, +0.9]s, dramatically increasing the number of leap seconds without violating the dUTC requirement. If the dUTC requirement is a bit more relaxed (say, [-2, +2] seconds) then we can even mandate leap second every year! But well no, I'm strongly against the current form of leap seconds because it is already problematic in the short term and will be yet useless in the long term. Recall that ΔT is expected to be quadratically increasing in the long term; this means that the effectiveness of leap seconds is limited to the point when any small fixed number of leap seconds per year (12 in the current system, but anything larger than 1 will cause a problem) is no longer sufficient, and that point is not far from the point where the magnitude of ΔT is significantly large and leap seconds are absolutely required. As DST demonstrates, the world is probably fine with ~2,000 seconds of ΔT, which wouldn't happen before 2500, but at that point we would already start using double leap seconds per year at average. We would probably abolish leap seconds for that reason alone.