As stated on Dunc'd On, yesterday morning Dallas had a rising star to build around in Doncic and a bunch of avenues by which to do so. Now they have essentially eliminated all other options to put all their eggs in the Porzingis basket. A huge gamble on an asset with multiple risks (health, attitude, and probability of re-signing). Part of the calculation has to be the difficulty of luring FAs to Dallas, but it seems too desperate by half.
NYK gets rid of said risky asset, clears a ton of bad salary from their books, gets two first-round picks (2021 is unprotected and is probably lottery), and a decent PG in Dennis Smith, Jr. Now they have cap space to sign two max FA, which may indicate that they already have assurances from one or more FA of their intent to sign.
It may pay off for Dallas but the risk/reward seems way too high, especially given the health of their situation before the trade.
Obviously the initial reaction was to tear into the Knicks, but now that the details are out I don't see how it is anything but a win for them, especially if they've been tipped off to KD's and/or Kyrie's intentions.