If it's true that Jaylen hasn't for a trade then I still think there's a decent chance he's simply back next year.
History tells you that to win the title you either need two all-nba level guys or an MVP + two all-stars in down years. Trading Jaylen Brown for a package like Trey Murphy + stuff essentially means you aren't a contender anymore, i can't see the Celtics being willing to do that.
That's why Jaylen for Giannis made sense, talent for talent. I haven't heard any other realistic deal that brings the Celtics back a player good enough to remain in contention and with three years left on Jaylen's deal there's no need to make this deal now unless you get that piece back.