The better question would be who trade for him? I've hear a few team but the market is slim. Also, Ainge has a bad a reputation with players and among GMs already would this make it worse?
I hate small guards. Some can play but they get exposed in the playoffs when teams play bully ball against them which they do and they break down.
How about Markkanen and Porter for Kemba. I say this assuming Markkanen would be a RFA which I think is true giving us the chance to overpay him if we want. Porter might help this season some but really the asset is Markkanen.
I was about to post a similar idea! TP! Here's what I had in mind.

Basically, it's Kemba + Thompson for Barnes + cap relief. As things stand right now, I don't think we can realistically expect to use the full TPE. The luxury tax would explode through the roof. Thing is, imo we aren't getting back enough value.
Alternatively:

PG: Smart - Pritchard - Teague
SG: Brown - Romeo - Green
SF: Barnes - Porter - Nesmith
PF: Tatum - Semi - Grant
C: Holmes - Theis - Timelord
We could even dump Theis for a protected first and move forward with Holmes and Timelord. I mean, CBS said he plans to limit the center rotation to just two players.