I think San Antonio and Boston make a lot of sense as trade partners, but I think there's fundamentally a close to 0% chance it happens in season. Massive trades like this are much easier in the offseason were teams have more cap space, more available roster spots and know where their draft picks will be.
but besides that, I think both teams are in an evaluation phase. For example, if Brown is going to play this well and stays healthy then by definition the Celtics window is wide open. Two all-nba level guys together is a clear contender in the East. San Antonio meanwhile probably wants more info on their young guys before they do a win-now trade, because if Harper is a 20-5-5 guy right away they aren't trading him for Brown, not given his age and contract situation.
In short, I think this is an offseason discussion.
