The third pick is still a nice asset to trade. In fact, a lot of GMs may consider the third pick to be more valuable than Tatum, considering Tatum himself was a third overall pick and only has two years left on his rookie deal. If Tatum had an amazing year things might be different, but right now he doesn't look like the sure thing, future all-star he did last year.
The Knicks also have Knox and Mitchell Robinson and would undoubtedly offer as many future 1sts as it would take, which somewhat matches our collection of crapola first rounders this year (in a draft most analysts say is shallow).
It's looking like the Celtics will have to offer everything they have now to win the Davis sweepstakes. I'm talking Smart, Tatum, Brown, the MEM pick, and at least two of our three first rounders this year. Even if it meant Kyrie staying, that would be a humongous risk to take.