Id imagine the Celtics two year plan is do their best to get out from underneath the Kemba contract while also trying to get a big, aiming in the end to grab Brad Beal when his contract comes up. Horford is a good example, of course, and would give the Celtics the stretch big they wanted, but I think the Celtics would first try to move Kemba for some smaller, more reasonable contracts. Horford would give them a hell of a lot of depth at the 5, a place where they sorely need it while they try to figure out if TL is ever gonna figure out his durability problem.
But guards of Beal's quality have also gone for relatively small chunks of change when ownership decided they weren't likely to resign the player, and as much as Beal talks about wanting to stay, I'd bet when the chips are down he moves on - that's often how it goes. Guy says he wants to stay, six months later he's on the move. Whether the Wizards see that is an open question. They don't seem to see that their defense is abysmal year after year, so no guarantees they realize this is their last chance to get some picks for him.
I wonder if Kemba plus a couple of picks or lotto tickets gets it done if Beal let's the ownership group know he's likely to leave. It took IT plus a pick, Jae Crowder, and Zizic to get Kyrie. About the same to get Mike Conley. Much more if the contract was longer: Houston got an insane haul for Harden.
The goal of course is to maximize Kemba's trade value. Horford doesn't do that. Rebuilding teams with huge contracts that are rapidly depreciating, who are also desperate for picks, are the best way to do that. There aren't many teams other than the Wizards in that position. Maybe GSW, but I bet they think they're resigning Steph all the way.