Honestly I don't really see a trade out there with Walker involved that would make the Celtics better (short term or long term).
What stars are even available? Paul (too much salary), Beal, George, Siakam, Simmons, Gobert, Vucevic or maybe Embiid? I'd love to get that 3rd young star, but Morant, Mitchell or Booker for example is not going to happen.
Middleton or McCollum are lateral moves. McCollum is just as much of a defensive liability as Walker is.
And I'm thinking that our offense would become even more stagnant with Middleton.
Playing without a true PG works for Dallas and LA because they have elite big playmakers in LeBron and Doncic.
Just watch how bad that offense looked by the Clippers and they had elite shotmakers, but not playmakers.
Which guard can we realistically obtain for Walker (+assets)?
Brogdon (injury concerns, good fit), Rose (only one year contract, older), VanVleet (do the Raptors want to trade to a rival?), D.White (huge gamble on our part), Fultz (another big gamble, funny one though), Holiday (I'd do that), Oladipo (love his defense, can he get back to his old self?) or LaVine (not a great playmaker, cheap perhaps).
But I do find that Walker is a bit of a problem. He's barely a top 10 point guard (it was kind of shocking to see how he got outplayed by Lowry and Dragic). Walker has injury concerns and when you take the contract in consideration he's below average in value per dollar return.
I'd take Curry, Lillard, Paul, Morant, Young, Lowry, Brogdon and Murray over Walker and I think Fox, Russell and Rose are on par him with (Irving and Westbrook are special cases).