Also as a gunner. I think we will see a lot of him.
His risk in the short term is getting hooked- same as every player. Longer term it's pass protection - if every time as RB he is going to run wide or be a slot receiver opponents will react accordingly. If he can block, he gets the chance to run and receive. If not, he eventually doesn't get the chance. Same thinking that applies to the whole offence - if you want to be able to play a passing game then you need a good running game.
Incidentally, the niners hardly passed in the pre season. Expect to see kapernick throw it a lot more right from week one. All those runs over the last 4 weeks have opened the opportunity to pass.