Based on the interviews from him and the statements made by Seneca Knight today, the coaching staff has penciled in Lucas into one of the starting guard positions along with AB. From the sound of the statements made since Lucas signed, it was one of the big reasons he signed with BYU.
It's not as clear whether Knight was promised a starting position, but he's clearly been told he's going to get a lot of playing time. One of his comments today talked about his discussion with the BYU coaches about what the schemes would be with him, Lucas and AB on the court at the same time.