I'm amazed some people want a period piece Superman. Yes, because Skycaptain was such a huge hit.
The difference there is people know Superman. That alone can get people to come to see it. Whether it is good, is a different question.
In any event, a period piece would be interesting. Although, like someone else had mentioned, maybe doing a Tim Burton with a modern setting, but with 30s style.
First off, Batman Begins was in flashbacks? I haven't seen it in awhile but it didn't look like flashbacks to me. Did I miss something?
When Bruce is training with Ducard, we flash back to the death of his parents up to when he throws away the gun and begins to work with criminals to understand them. By the time Bruce burns down the League of Shadows HQ, the flashbacks are done (save for an emotional point callback towards the end).