It certainly will be interesting to see how much Kapler uses his bench. McCutchen is known for his durability, so I don't think Williams will start too much there if Cutch is playing well. Altherr and later Quinn might get some CF starts, especially if Odubel is struggling. As for the other spots, Realmuto will play about as much as any starting catcher (140 games?) and Franco does not seem to be wanting to give too much time to Kingery. Segura is also very durable.
We may be looking at a bench that plays much less than the bench last year. With only 4 of them they'll pinch hit a lot, but is hard to see them getting too many starts absent injury. I imagine they'll get Williams and Knapp a start in the MN series. The first LH starter we face is not till the 13th, so we may not see Altherr either.