As of April 1st, in the OCG ONLY, Fusion, Synchro and Xyz monsters will be summonable to the Main Monster Zone in addition to the Extra Monster Zone. The rules for Link Monsters will remain the same. You are not limited to 1 of each. For Pendulum monsters, they are almost identical, with one small change: Face-down pendulum monsters in the Extra Deck such as Nirvana High Paladin can be summoned to any zone the first time, but when pendulum summoned back to the field from the face-up extra deck they still must be summoned to the Extra Monster Zone, or a zone a link monster points to.
The name for this update will be “Master Rules (April 1st 2020 Revision)” (not Master Rules 5 or 6 or New Master Rules 2).