Lyles' ceiling is pretty high, imo. If he can really shoot well enough, get stronger and put in effort on defense, he could be a really really impressive player by his 21st birthday. Maybe like a Lamar Odom with better IQ.
Depending on how well the Jazz switch on defense, Lyles could conceivably play some significant time as a big-SF, a bit like Donyell Marshall, Andrei Kirilenko or Odom. It's all about his shooting and reactions on defense. It's not perfect, but with Gobert, Favors and Exum on the floor, there wouldn't be major holes in our defense. ...And our rebounding could be really special. Then you could play Hayward or Hood as the other wing.