Threads has implemented both ActivityPub implementations of quote posting: it uses the Misskey quote posting system, and also implemented fep-e232 (which is a better version of quote posting, but not implemented by any major platform), so that they are already immediately compatible with platforms that use the FEP version.
Mastodon ignores the current implementations of quote posting, and wants to do their own new implementation so that they can add granular control.
piefed has quickly become my main threadiverse driver. its really nice