Okay, so money wise I think a Brogdon+Gallo package would work money wise. Lets assume those two are shipped to a third team for assets that are flipped for KP.
At that price the deal makes SOME sense. KP opts in for next year at 36 million and becomes an expiring. Celtics get more expensive for NEXT year but get off the 22 million for Brogdon in 24-25, when Jaylen's extension kicks in and they become FAR more expensive. Its sort of a 1 year gamble on a guy who will still be only 28 next year. Unlike a guy like Ayton, KP is a good enough shooter that you can probably play any two of Horford/Rob/KP at a given time so having too many center isn't AS big a deal.
If all you give up is Brogdon+ other small asset or equivalent I'd like it. It simplifies the Celtics contract situation going forward and really beefs up the center position.
Remember, most of the reason the C's want to trade Brogdon is they don't want the extra year of his deal on the books when Jaylens contract kicks in. Shifting that to a guy essentially on an expiring makes sense.