Personally, I'm against having an unlockable character. Firstly... Well, we can make our own custom characters as we wish, and download each other's, but I understand that's not a proper reason. Secondly, how would that even work in multiplayer?
- If we say "if the host has it, everyone has it", then everyone who hasn't unlocked it will be confused, due to no mods being added, and if the host doesn't have it, those who have unlocked it would be confused about not being able to play as the unlocked character.
- If we say "everyone can use it", again, everyone who hasn't unlocked it will be confused, especially if that includes the host who didn't add any mods.
- If we say "noone can use it", that's pretty bad against everyone who has unlocked it, especially if everyone on the server has unlocked it, even more so if it's a private co-op server with a friend or something.
- If we say "everyone who has unlocked it can use it", we again come to the confusion for those who haven't unlocked it, and especially if the host hasn't and sees lots of the unlocked character in a mod-free game where the host is entirely unable to use that character.
- If we say "the host decides it", then that'll either allow them to use the unlockable character before unlocking it if the host always decides it, or be perfectly fine if the host only decides it if they've unlocked the character, but in both cases, we again come to the problem of players who haven't unlocked the character seeing the character in a mod-free server.
- If we go "if everyone has it, everyone can use it", that means there could be people playing as the character, then a person without the character could join and "rob" them of the character.
- If we go "non-multiplayer"... That's definitely just the wrong decision.
In short, there is no correct way to implement it for multiplayer, and it's also wrong to make it single-player only, not to mention the burst of extra emblems from record attack when the character is unlocked or the lack of record attack with the character. All of these things can be overcome by just only having the normal 3 characters unlocked at all times, and using custom characters for other characters if wanted.
...Besides, why's all this "unlockable character" speak even in the 2.2 teaser thread, rather than some suggestion thread? (It's too discuss-able to be put in the "Suggestions" thread itself, of course.)