Simmons not being able to play right away and/or having to shake off rust isn't really an issue. I know Vivek wants to win now, but with players dropping left and right due to positive COVID tests, Holmes being in and out of the lineup, potentially a deal for Hield and/or Bagley, this team is not headed for the playoffs with or without a shakeup.
So if the team traded for Simmons, the fact that he'd likely miss a few games and then have to round into shape isn't really a big deal. It adds ping-pong balls and gives him all the time needed to acclimate. If the Kings were to play well at the very end of the season (generally fool's gold) it would at least give hope moving forward which is what Kings fans need and currently don't have.
I previously said that I'd keep Hield if Simmons was dealt for but I think that really depends on what his mindset/attitude is. Is he a malcontent/unhappy and desperately wants out? If so, deal him if there's something of value to be gotten. Trade Bagley if there's any interest. Deal Barnes to a team that needs a 3/4 wing for their playoff push (Atlanta maybe?) and even deal Holmes if the right deal comes along.
I don't think the Kings have the pieces to get Turner without giving up FRPs but Indiana has lost 6 straight and needs a shakeup. Plus Turner is a FA after next season, making this the time to move him. If the Pacers were willing to take say Barnes & Holmes for Turner and Warren and the Sixers would take Fox for Simmons you'd have:
C Turner/Thompson/Len/Jones/Queta (why so many bigs Monte?)
PF Metu or Harkless/Woodard
SF Simmons/Warren/King
SG Haliburton/Davis/Ramsey
PG Mitchell
Plus whatever you could get for Buddy and/or Bagley - ideally a backup PG and a wing who shoots well. That team needs shooting and roster balance, but would likely be drafting in the 6-10 range where guys like Keegan Murray, Kendall Brown, Nikola Jovic, or even Patrick Baldwin if he starts putting it together.
Turner
Simmons
Rookie SF/PF
Haliburton
Mitchell
Is a pretty solid starting five with solid defense and enough shooting to cover for Simmons. You can stagger your best playmakers in Haliburton and Simmons to maximize both.
Probably a pipe dream on both trades honestly, but I'd greatly prefer that team to what we have now plus another mid-to-late lottery pick.
I don't think that's enough value for Turner, and I don't think they'd be interested in Holmes as they'd want to play Sabonis as a full time C after Turner is moved and find a PF who can space the floor and defend.
I think you could arrive at a similar team with these moves:
TRADE #1
PHI Gets: Bradley Beal
PHI Gives: Ben Simmons
Why for PHI? Get a star talent in exchange for Simmons who fits perfectly next to Maxey, Green, Harris, & Embiid in an effort to bring a championship to Philly.
PG - Maxey / Curry / Springer
SG - Beal / Milton / Joe
SF - Green / Thybulle / Korkmaz
PF - Harris / Niang / Reed
C - Embiid / Drummond / Bassey
SAC Gets: Ben Simmons, Davis Bertans, & Raul Neto
SAC Gives: De'Aaron Fox, Marvin Bagley, & Tristan Thompson
Why for SAC? Balance the roster by swapping Simmons for Fox while improving the defense. Bertans would also be an interesting piece to complement Simmons (despite him being a negative value contract).
PG - Mitchell / Neto
SG - Haliburton / Davis / Ramsey
SF - Barnes / Hield / Harkless / Woodard
PF - Simmons / Bertans / Metu
C - Holmes / Jones / Len
WAS Gets: De'Aaron Fox, Marvin Bagley, & Tristan Thompson
WAS Gives: Bradley Beal, Davis Bertans, & Raul Neto
Why for WAS? Beal chose to not sign an extension with the Wizards and could walk at the end of this year. The Wizards get a 24 year old PG locked in for 4 more seasons while also moving off of Bertans contract to help with a rebuild/retool.
PG - Fox / Holiday
SG - Dinwiddie / Caldwell-Pope
SF - Kuzma / Avdija / Kispert
PF - Bagley / Hachimura / Gill / Todd
C - Gafford / Harrell / Thompson / Bryant
Trade #2
IND Gets: Harrison Barnes & 2022 SAC 1st (Top 4 Protected)
IND Gives: Myles Turner
Why for IND? Barnes gives them a SF/PF to better space the floor next to Sabonis while also picking up a 1st round pick to further add to their core.
PG - Brogdon / McConnell / Sykes
SG - LeVert / Lamb
SF - Duarte / Holiday / Martin
PF - Barnes / Craig / Brissett / Warren
C - Sabonis / Bitadze / Jackson
SAC Gets: Myles Turner
SAC Gives: Harrison Barnes & 2022 SAC 1st (Top 4 Protected)
Why for SAC? Land a true rim protector to play alongside Simmons. He also is a solid shooter from 3 allowing the Kings to give Simmons optimal space to operate.
PG - Mitchell / Neto
SG - Haliburton / Davis / Ramsey
SF - Hield / Harkless / Woodard
PF - Simmons / Bertans / Metu
C - Turner / Holmes / Jones / Len
Trade #3
CHA Gets: Richaun Holmes
CHA Gives: Ish Smith & PJ Washington
Why for CHA? With Hayward, Bridges, & Oubre on the roster, Washington is expendable. They move him while substantially upgrading their starting C.
PG - Ball / Bouknight
SG - Rozier / Martin
SF - Hayward / Oubre
PF - Bridges / McDaniels / Thor
C - Holmes / Plumlee / Richards / Jones / Carey
SAC Gets: Ish Smith & PJ Washington
SAC Gives: Richaun Holmes
Why for SAC? With Turner on the roster, they move Holmes for a SF/PF who can space the floor & defend next to Simmons.
PG - Mitchell / Smith / Neto
SG - Haliburton / Davis / Ramsey
SF - Washington / Hield / Harkless / Woodard
PF - Simmons / Bertans / Metu
C - Turner / Jones / Len
Mitchell-Haliburton-Washington-Simmons-Turner would be a very strong defensive team. In fact, Mitchell, Simmons, & Turner would all likely be in the conversations for the All-Defensive year after year. On top of being an excellent defensive team, Simmons is surrounded with shooters (Mitchell, Haliburton, Washington, Turner, Davis, Hield, & Bertans) to hopefully unlock his full potential. Lastly, that starting 5 is young and still has time to get better. Mitchell is 23, Haliburton is 21, Washington is 23, Simmons is 25, and Turner is 25.
Long story short, I think this improves our chances of making the playoffs this year, dramatically improves the defense, and still gives us a relatively young core to improve/grow over time.