I'm not sure if Ainge would give up Brown for a rental year of Leonard, but I'm a little surprised that so many people think it's out of the question he would do it.
My feeling is that Brown is a borderline all star, which might be why I feel like he's not untouchable. I really like him. He's young, aggressive, and chocked full of potential. I think his floor is Luol Deng, and despite Deng's current albatross contract and crumpled body (Thibs!), he was a really good player for about a decade. Somewhere between Luol Deng and Kawhi Leonard feels like where he'll end up.
That said, a healthy Kawhi on the C's next year puts us at the level of the Warriors and that just isn't something you pass up. Even if Kawhi leaves in 2019 we'd get a really good shot at #18 this year, potentially a better shot that we'd have in any of the subsequent years with Jaylen.
I'm not saying I'd do it, but I'm saying I don't think it's as outrageous to consider.