I disagree, people want secret characters they just don't want to pay for them.
By having the game come out with one unlockable character they could be a good way to show even the people who've missed all the news what's happening with the characters this time.
The very first thing they should see is that locked character and told explicitly how to unlock them. you need to get that info out before they stumble across the bad info and start screaming about on disc locked characters.
Then you end up pissing off the community that actually told you not to do this kind of thing.
Honestly, aside from the pay option, the only other way to handle locked characters, is to make them
unlocked by default in versus mode like Skullgirls (where the two "locked" characters are only locked in singleplayer/story modes).
I don't think anyone would be silly enough to spend money on a character when they could simply work to unlock them...just like the good old days
You forget about tournament organizers and players who simply want to use a character for competition without having to spend pointless time in singleplayer.
Also, I know a good number of people (including Skullgirls lead developer Mike Z) who, when presented with the option to either unlock or buy, simply opted to buy the content because they found the idea of having to play singleplayer to unlock content for multiplayer stupid.