Look, the position that Mo will likely play isn't going to be rocket science. You'd have to be a lousy coach to not have him be effective with a year under his belt, and we don't have lousy coaches.
He's an enormous man and his body only has so many years to play football. If BYU coaches really are serious about developing NFL players, Mo isn't going to be a 6-year project, languishing on the sidelines for two years... and if he plays anything like I think he can, he'll be an NFL draft pick before he plays 4 years at BYU.
The NFL isn't nearly as excited about undersized guys with tons of skill as they are about athletic freaks who they believe they can develop. You can't teach size.
Just my personal opinion, but I'd let Mo run it on short yardage situations this year. Have Tanner point out which gap to him. Honestly it may not even matter. In practice develop him into a unstoppable 1-technique DT. Teach him three moves and help him master those over the course of a year. Then next year unleash the beast.
...and still feed him the ball on the goal line, especially late in games... can you imagine being a tired linebacker in the 4th quarter of a game and seeing 400+ pounds of bad intentions lined up in the backfield? Hahaha.