Summary
Ntilikina came into the league being seen as a point guard. However, due to his lack of ability to create off the dribble, Ntilikina's best role is likely as a 3-and-D wing. However, Ntilikina is a career 34% three point shooter, so he certainly needs to make shots at a higher rate in order to fulfill that kind of role.

Ntilikina will still only be 23 this summer when he hits free agency. The possibility of Ntilikina becoming a star is likely gone, but there could be a valuable player in there somewhere. Could he be similar to Kris Dunn, but a slightly worse defender and a better shooter? I think that's reasonably possible. 
 
Cap Considerations
Ntilikina will be a restricted free agent with a $18.5 million cap hold and a $7 million Qualifying Offer. If the Knicks do not have interest in bringing back Ntilikina they could refuse to tender him a QO, making him an unrestricted free agent. With Ntilikina's QO being on the higher end, I think there is a possibility this occurs. However, the Knicks may have so much unused cap space that they don't mind if Ntilikina signs the QO. If Ntilikina is re-signed on a multi-year contract, front-loading the contract could be beneficial, as the Knicks have plenty of space now.

Other teams will have multiple ways to sign Ntilkina as even teams without cap space could possibly use either of the Non-Taxpayer MLE, Taxpayer MLE, or possibly even the Room MLE to sign him to an offer sheet. However, Ntilikina being a restricted free agent would greatly lower his interest among teams, as they will worry that the only way to pry him away from New York would be to significantly overpay him.