CleverNickName
Limit Break Dancing (He/They)
If they put those "optional" rules in the Player's Handbook, yes. For better or worse, all of those so-called Optional Rules that get printed in the PHB (feats, multiclassing, variant humans, etc.) become 'the law of the land' and all players will assume that they are available for use in all campaign settings. It creates a lot of work for DMs who do not wish to employ those rules in their games. (Ask me how I know!)The fact that those "optional" rules immediately became the law of the land moving forward makes that claim by WotC suspicious.
Meanwhile, all other optional rules (Spell Points, Renown, Mixing Potions, etc.) that were printed in the Dungeon Master's Guide are not assumed to be ever-present and available...they languish unnoticed in the DMG, barely read by anyone. Players don't build their sorcerers with the Spell Point variant without checking with their Dungeon Master first, and they don't automatically start rolling on the Spell Mishap table when they botch a spell scroll.
All that to say: if a rule is to be truly optional for all games, it cannot be printed in the Player's Handbook. Otherwise, it's not really an optional rule.