He's actually 297lbs right now, they said it a few games ago during the broadcast.
His potential is top 5 player in the league, depends on if he puts in the work and focuses on the low post. There isn't a better "blank" sheet of paper in the NBA right now, his combination of speed, agility, hands, coordination and sheer weight don't come along very often. The thing that sets him a part from the DeAndre Jordan/JaVale McGee types other than 30lbs are his legs, his lower body is one of the major reasons why he rebounds so well. Once he roots himself in the paint he's difficult to move, same reason people have trouble backing him down.
The Pistons strength and conditioning coach has said they want him to add upper body mass, and Joe Dumars has been saying if he can get some Shaq like moves he could be unstoppable. I haven't been this excited over the development of a frontcourt player in a minute, especially if they're looking to pack on more weight and using Shaq as a template.
At bare minimum he would already be a double double guy this year if he got starters minutes, it's not a stretch to say he's better than Jordan or McGee already.