But standards need to be made eventually based off something, or Fediverse will fail to deliver on its promise.
That’s what the FEP (Fediverse Enhancement Proposal) system is for.
Piefied is the only project among the three (Lemmy/Mbin/Piefed) to give a list of supported FEPs.
That’s not correct, it does have an app (Interstellar).
Not official, but neither are all the Lemmy apps.