First, why would you assume it would be 1 year? Second, that team is much better than the current roster this season (and for the foreseeable future) and it isn't close? Jimmy Butler is a much better player than Jaylen Brown. Sure at some point in the future Jaylen Brown will pass him up, but that doesn't mean Jaylen Brown will ever be as good as Jimmy Butler is right now. And Jimmy Butler's age is much more inline with Irving, Hayward, and Horford. Boston should absolutely capitalize on the prime of those 3, rather than hoping that someday Tatum and Brown can be a championship level core.
I'd acquire Butler and wouldn't give it much thought. He is a very good 2 way player in the same tier as Irving and Hayward in the league.
It would probably mean that Horford would have to be traded next summer, but I'm ok with taking the championship shot this year.
And I would absolutely trade Brown in the trade if that is what it took.
So basically Butler for Brown, Morris, Yabu, and Nader (I think that is enough salary but if not add Semi).
Post-Trade - Main 2 deep rotation
PG - Irving, Rozier
SG - Butler, Smart
SF - Hayward, Tatum
PF - Horford, Theis
C - Baynes, Williams
That team if everyone is healthy and back to where they were would be a real threat to the Warriors and the very heavy and clear favorites in the East. Even if the Sixers acquired Leonard (for basically Saric, Covington, and 1sts) that C's team would still be the favorites in the East.
I'm not mortgaging a potential Eastern Conference / NBA dynasty for 1 year of still-underdog contending status against Golden State. That roster won't win it.
If Kyrie insists, then we can get a lottery pick + at least 1 good player or prospect for him.
Plus Smart, Williams and our Kyrie haul is a very good and still young core moving forward.
We'd also have 3 good-to-elite lottery picks (Sacto, Memphis, Kyrie lottery pick) to use or roll over to ideally go after a PG, a big and another wing. Personally, I don't think Rozier is the answer at PG, and I'd like a PF/C to hedge against Robert Williams not turning into Capela.
EDIT - I would try to keep Kyrie here at nearly any cost- except trading JB or JT.
This is the age old debate, get vets in here now by trading young talent, or develop the young talent over time.
There's no right answer of course but given that I'm personally more invested and excited about the Tatum-Brown timeline than I am about the Horford-Hayward timeline, I will be patient. But that's just my personal preference.
I totally get that, but exciting young players often don't develop into what they could be or they could get hurt or they could leave before they are truly ready to compete or they develop well but the team around them isn't good enough or they develop well but just run into a better team.
I'd much rather elevate the current team, which many feel is the best team in the conference already, and take a real shot over the next 3ish seasons (while still keeping Tatum, Smart, Sacto, Mem, etc.). While I'd favor a healthy Golden State against a Boston team comprised of Irving, Butler, Hayward, Tatum, Horford, Baynes, Smart, and Rozier (with Theis and Williams for big man depth), I'd give that team a real shot, and I think there is a very good chance this is the last real year that GS is what they currently are (I don't see them keeping Klay and Dray and frankly Curry and Durant are aging with health concerns). When a team is close, getting it closer makes far too much sense to me.