Nesmith will be a rotation player for the Cs by the end of the season. He's a hard worker and smart player. At this point, his reaction time on rotation defense is probably not as quick as Semi's. Offensively, he's a bit too erratic. Reps in practice will get him confidence and improve his reaction time.
He'll earn minutes like Langford did last season. Langford earned 14 seconds total in his first 24 games. The thing about Nesmith's game is that if he can figure it out defensively like Langford did last season (and I think he can), he will be a much more valuable offensive player. Langford's best offensive skills are when the ball is in his hands a good amount. Imagine having Nesmith hitting 45-50% from the corner three instead of 19% like Langford. That not only is good production, but it would definitely open things up for Tatum, Teague, Brown, and Walker.
I have high hopes for both players. I think it is possible that by the end of this season, the Celtics could be one of the deepest teams in the league with some of the most intriguing young talent.