The thing about trading for BI is that he is going to want the max or close to max contract to re-sign. It would put the Kings in salary cap hell for years. I'm not sure a core of Fox-Sabonis-BI would be title contenders.
It may be better to go after a more cost controlled player (i.e. Grant William, Jermai Grant or even Kuzma) to fill in the stretch 4 and allow Keegan to blossom, rather than to mortgage the whole salary cap and future that BI is the missing piece to a championship.