I don't see anything wrong with promising early playing time, generally speaking, it depends.
An example, I know Myles Brennan's dad asked for the cookie monster's word that Myles would get playing time his freshman year in meaningful situations. They (his dad and him) wanted to evaluate whether Myles could compete in the SEC and whether LSU was a good long-term fit. The cookie monster had him in the first half against Bama at Bama. I saw nothing wrong with it, I can kind of understand as well... why ride the bench somewhere 3-4 years only to find out you really can't play in the league.
Now promising starting spots...ehhhh probably not a great idea.