I'm not ready to just salary dump Walker, but if that time comes, I was trying to think of some interesting trades to do so and I came up with this 3-team trade, which I think would on some level work for all 3 teams.
Boston - Rubio, Payton, Burks, Layman
New York - Walker, Ojeleye, Green
Minnesota - Ntkilina, Bullock, Brazdeikis, Edwards
No picks going anywhere except maybe a 2nd rounder or two
Rubio is signed through the end of next year but makes about half of what Walker does. He isn't a scorer, but is still a solid playmaker. Payton is currently starting for the Knicks, so between him and Rubio, Boston has at least a respectable PG rotation (Smart moves over to SG full time). Burks provides some much needed wing shooting off the bench (40.7% on 4.8 attempts this year) and Layman is a youngish SF that can play in the rotation if needed. Boston also adds a bunch of salary cap room, making it easier to use the TPE before approaching the tax or the apron and also adds another 8-9 million TPE as well (for more flexibility this year). Boston is probably worse this year, but not appreciably worse unless Walker really turns it around, but the trade provides a lot more long term flexibility and a lot more options for using the big TPE this year.
New York gets a, when healthy, legit lead guard to further their playoff push, and gets to keep Randle and all their prime players/assets to do it. They have to believe Walker will get better as he gets healthy to take on the salary, but I think it is something they would do. New York has about 17 million in cap space, which is why they can take on all that extra salary this year and why the trade works just fine under the rules.
Minnesota drops a ton of salary getting below the tax this year and shaving a bunch off the future and gets some players to look at as potential long term rotation players. Though this is a pure salary dump for them.
So Boston post-trade
PG - Rubio, Payton, Pritchard, Teague
SG - Smart, Burks, Langford
SF - Brown, Nesmith, Laymon
PF - Tatum, Theis, G. Williams
C - Thompson, R. Williams
TW - Waters, Fall
Again a team that is probably a bit worse this year (but we aren't winning the title anyway), but you do the trade for the long term flexibility it provides and the more options opened for using the TPE (and the new TPE just created).