Cons: It takes a while to train guard skills at 6'8", JS will take a good season to get to a decent level, and he'll never be overly dominant.
I like balanced bigs, and I train them myself, but don't neglect big man skills totally. Maybe train guard skills half of the time, and with him being an allstar, you can have a nice big who's still 13/13/13 or so inside before he caps out.
I agree though, don't stick to IS/ID/REB. I just wish he was either shorter or taller. 6'8" is a pain in the ass height.