Rob Seaman quoted:
(after 0000 UTC 21 December of the transition year)
The difference of UT1 from UTC should not exceed ±1h.
2 Adjustments to UTC
2.1 Adjustments to the UTC time-scale should be made as
determined by the IERS to ensure that the time-scale remains within
the specified tolerances.
2.2 The IERS should announce the introduction of an
adjustment to the UTC time-scale at least five years in advance. At
the time of the announcement the IERS should provide directions
regarding the details of the implementation of the adjustment.
2.3 All operational rules and nomenclature prior to 0000
UTC 21 December of the transition year given above no longer apply.
NOTE 1 – The broadcast of DUT1 will be discontinued.
NOTE 2 – Predictions of the Earth’s rotation currently indicate that
such an adjustment would not be required for thousands of years.
There's nothing in this text which would stop the IERS continuing
to issue leap seconds as they do now except they'd have to do it
five years in advance so would, presumably, have to relax the ±0.9
seconds requirement somewhat.