At one point they opened their messenger system and allowed XMPP clients to connect. This worked absolutely fine, and chatting in any XMPP compatible client was possible.
But it was also possible to OTR encrypt the data so Facebook only got seemingly random character strings that are absolutely useless for data harvesting and profile analysis to sell to advertisers, so they closed down the messenger and disabled the XMPP bridge not long after they opened it.
Same will happen here: As soon as people start interacting in a way it is not possible for the company to track everything, they will stop allowing it.
On a personal note: I will defederate from Meta as soon as they establish their ActivityPub bridge (it of course will only be a bridge, or does anyone really think they would base one of their main features on an open standard?)