Okay, now, the way I see it, there are two possibilities.
1. The fact that a total newcomer was announced before we had Meta Knight or Snake's profiles means we're getting starting characters before secret characters. Ridley won't be appearing for a very long time. The "Warning: New Challenger Approaching" could easily just mean new to the game rather than signifying an unlockable character.
2. Sakurai is announcing the more likely characters first and saving the suprises until later, regardless of unlockable status. Fire Emblem characters were secret in Melee, and Sakurai hasn't hesitated to show secret characters early before. We haven't seen Meta Knight and Snake yet because he is wacky and unpredictable. Many people expected a new FE swordsman to replace Marth and Roy (sorry Silver, but that's my prediction...multiple swordsman in reference to a game that's all about the balance of three different weapons is a waste of potential), and since Ike will have been in multiple games and is well-known in both the U.S. and Japan, he was the most likely candidate. In this case, Ridley will probably be one of the next three or four characters announced (I'll bet Krystal and Dedede wouldn't be too far off either).
...I guess that really isn't too helpful after all. Oh well. Even if Ridley isn't announced for a long time, if we see an Artifact Temple or Ridley's Lair stage announced that doesn't have Ridley in the background, that's as good as a confirmation for me.