If KP takes his option, Boston needs to add more salary than just Brogdon to make it work. Williams SnT could fit nicely, with Mavs sending some salary to Washington. Since I don't think 2023 picks are involved in this deal anyway, I think they could afford to wait 10 days
Edit: or they just add Gallo and Muscala and it works financially.
Edit: or they just add Gallo and Muscala and it works financially.