At 3B sure. Like I clearly stated: what about 2B?
Referring back to last season, seems like they could have played him and showcased him to deal this off-season. Now he's just going to age off of being a prospect.
Edit: oh wait, you mean Gunnar for SS next year.
Point still stands: he can play 3B then until Holliday is ready.
Urias (wasn't that good last year) and Mateo (utility player at best) shouldn't block any of the younger guys from playing.