Will the first secret chapter be available for all players? And will there be any second secret chapter?
Quick answer: 1)Yes 2) Nope
The first secret chapter: Lost Memories, is unlockable for all players and game versions after finishing it. As for the "second": Unveil the truth starring Della Hudson (the journalist), there's no intentions of doing it.
And if you are trying to figure out why, I'll help you (⌒ω⌒)
"Unveil the truth" changes the core and game mechanics and adds a lot of new dialogues in six languages (english, spanish, french, german, portuguese and russian).
For this chapter there'll be about the same amount of words as for the main game (it makes it a game by itself) and the budget for translation is very tight so we can not afford the cost for the Della's chapter.
Now maybe there are people thinking about dropping one or two languages options to get the chapter but we don't agree with them and it'll be a long story so PLFC will come on those six languages and every player will have the chance to play the chapter Lost Memories if they beat the game (〜￣▽￣)〜