I think Willson, McGrath, Harper, and Jesse Williams
I don't think Christine Michael is going to get enough carries to make much of an impact, if he does anything, it's on ST, but you have Harvin returning kicks and Tate returning punts.
Speaking of which, I see Tate doing much better on PR duty than Washington; he's much harder to bring down and more elusive, but doesn't have the top end speed. Tate will have a much higher average than Leon did, but probably won't have as many really long returns.
Jessee Williams will make an impact as he will get playing time in the DL rotation. I forget the kid's name from Penn State we drafted, but I see him making the same impact, albeit from one position where Williams will probably get moved around.
Harper will make an impression as he will get some reps when Baldwin inevitably gets hurt. His size and physicality will mesh well with RW's style of not being afraid to let the receiver make a play. Man, I really wish BMW would've made it long enough to play with Russell Wilson. Wilson was throwing jump balls to Tate and Baldwin...BMW would've owned some fools going after those balls.
Willson/McGrath also to make a big contribution. I don't know if one will really shine over the other until after TC, but the oppportunity is there for someone to get serious playing time with McCoy out.
I'm very interested in seeing what Simon will bring to the table, but he's been injured the entire offseason, so he has a lot of catching up to do. IF he can get healthy, he's in the deepest position on the team. I'm not really sure he sees any playing time this year, but I'm theorizing PC didn't really need to see much out of him.