I've just seen a quoted reply by an Akkoma user.
Curiously, these messages mark the replied post differently (i.e. not using an inReplyTo field, but a quoteUrl one). I don't know if this is an ActivityPub standard or a private extension.
Anyway, I'll write it in the TODO file to take a look at it in the near future.
Thanks for the suggestion.
CC: gyptazy (npub1qw7…q0ue)