My understanding of the argument here, which seems to make sense to me, is that the AMP already introduced a significant breaking change with regards to monads. Books and lecture notes have already not caught up to this, by and large. Hence, by introducing a further change, which _completes_ the general AMP project, then by the time books and lecture notes are all updated, they will be able to tell a much nicer story than the current one?
~/personal/src/snap λ find . -name '*.hs' | xargs egrep '#if.*(MIN_VERSION)|(GLASGOW_HASKELL)' | wc -l64