Board Thread:General Discussion/@comment-28869007-20160628155628/@comment-24674051-20160702204318

Even a backdoor pilot that showed future events could have a somewhat spoiling effect on the present day storyline.

Showing, or even teasing, future events is actually one of the things that caused a lot of confusion when Will as brought to the main cast in season 4. The end of Wonderland teased about a future event that hasn't happened yet, and Will's appearance, and his untold story, sent some signals that clouded the future tease. (and things are still not totally resolved from that decision).