So just in general, this is what I think will happen.
As I've said many times, my preference is adding D'Lo + 2 decent centers.
What do I predict actually happens? Kemba stays in Charlotte, and the Celtics sign sign Vucevic + trade for Eric Gordon + use room exception to add another cheap, depth center.
Eric Gordon might sound surprising, but he's available and honestly he'd be the perfect fit on this team I feel. Might be that underrated move that looks like a "steal" when you look back. And I think we can absorb his salary in a trade too unless Vuc actually gets a deal larger than 25M AAV (and I don't think he will).
We all talk about how the team (especially bench) can be prone to scoring droughts. Gordon is capable of scoring in bunches and is a bit underrated. At his current contract, he's looked fantastic. And you'd still have Brown + Smart getting a bigger role and a chance to keep improving too.