I feel certain that Felix Felicis is either the name of the "lion-like person" described in the previous clue left by JKR or related to Crookshanks.

If it is the "lion-like person" it may well be the "Half-blood Prince" and/or something related to Godrick Griffendor.

On the other thand, I am quite sure that Crookshanks is going to play a VERY important role in the future, but I am not quite sure what it will be. This could be "Crookshanks' chapter.