Note, that #Jabber has message replies and message reactions since some time now. Replies are implemented at least in #Dino, #Gajim, #Kaidan, and #Prose. Reactions are implemented at least in #Conversations, Dino, Gajim, Kaidan, #Movim, and Prose. Probably more.
TTBOMK, the #XMPP protocol itself has threads since ages, but I'm not aware of any implementation in a client. @prose is working on it, so I heard.
