No invalidation would be happening now, merely a note in the coming standard
that the %b in printf(1) would (might) be removed in a later version of
the standard - so implementations have time to implement something to
replace it, and applications to stop using %b in printf(1). The next
version of the standard isn't likely for at least another decade (the
coming one isn't finished yet, and that's not the next that counts here,
and later issues that are merely corrections (TCs) don't count either).
[As a reference for timelines, the current POSIX standard is from 2008,
though a couple of TCs have followed it - that's 15 years already
between versions.]