theoretically he could opt into the last year and then get traded. I believe the new team could then extend him. I mean that is basically how he ended up in Houston. So some sort of package centered around Kemba could theoretically be possible. No idea why Boston would do that though.
2021 Historical Draft - 5th Pick - Raptors
PG - Tiny Archibald 73, Don Buse 77, Terrell Brandon 96
SG - Chet Walker 67, Michael Cooper 87, Raja Bell 06
SF - Predrag "Peja" Stojakovic 04, Kiki Vandeweghe 87, Robert Covington 18
PF - Karl Malone 97, Spencer Haywood 73, David West 08
C - Ben Wallace 04, George Mikan 50, Al Jefferson 08