“It is proposed to change the main key for archaeological sites from site_type=* to archaeological_site=*.”
This means historic=archaeological_site + archaeological_site=* is now the approved way to tag archaeological sites, and it means that site_type=* on archaeological sites is now deprecated in favour of archaeological_site=*.
That seems to be out of scope for the approved proposal.
However, there are a few fortification_type tags which can be already re-tagged with the approved defensive_works=* tagging scheme.
The relevant guideline for this is Any tags you like.