San Antonio got Fox without giving up anyone. And based on their last two trades, Boston's new ownership appears to be more interested in cutting costs than competing right now. Jaylen Brown is around the same level of player as Fox ... a guy who might make 3rd team All-NBA if everything breaks right. He's being paid MVP level money though so that depresses his trade value a bit.
If I were Boston I would ask for Keegan of course but I don't think we should include him in any trade unless we're getting a true MVP level guy. Otherwise we'd be giving up our best young talent to wind up exactly where we are now as a middle of the road team without a lot of assets to build with. That's ultimately going to set us back even further.
And I say that as a huge Jaylen Brown fan. He's probably my favorite non-Kings player in the league right now, but not entirely for basketball reasons. I would love to see him playing for Sacramento but it needs to be as part of a big two with Keegan while Scott Perry figures out the rest of the roster, not as a big three with Sabonis and LaVine.