I think the coach's job is to take what he has on his roster and figure out his rotations and gameplans based on what will make the team as competitive as possible.
It's the GM's job to give the coach a roster that fits the team's long term goals, whatever they may be.
So I think that Brad Stevens should play the guys he thinks are most deserving of playing time, and who will help the team play the best basketball.
It's Danny's job to not give him too many veterans or whatever if he doesn't want the team to win "too many" games.
But really, to answer your question more specifically, if this really young team, while playing the young guys who work for and earn spots in the rotation, wins a lot of games and even makes the playoffs, I won't be unhappy. Because that would mean we already have a much better talent base than I thought (e.g. Olynyk and Sullinger are ahead of schedule / even better than expected).
I'd be pretty surprised if that happened, though.
I'm definitely NOT in favor of force-feeding young players minutes even when they aren't ready or there are more deserving, more polished players behind them. That sends a terrible message to the young players about how hard work is rewarded on this team.