Will buying the Expansion also include the game?

[Tiggy]

There is no possible way for us to know the answer to this. All we can say is that it might have a bundle and it might not, but it will definitely have a stand alone version for those of us who already own the game.

[Freyt]

Stuff

Leon was actually an evil Dark Knight before he joins as your final party member (FF2). I don't know of any Dark Knights that use the black magic ability, if you're saying they use abilities that would normally otherwise be black magic then that makes sense, other than that I haven't played FF11 so if they use black magic there then okay. Dark Knights use the power of darkness to fight which the first ability to that was Souleater, though it's worth bringing up that the magic knight from FF3 was rewritten into Dark Knight for the 3ds remake, and used dark swords in order to combat multiplying enemies.

[Akiza]

Dark Knight uses gravity, slow and dark spells.

[Zooters]

As it stands Dark Knight would need something levelled to access it even beforehand.

Actually no. None of the new jobs have any base class and Yoshida said Dark Knight would be available to play out of the gate with the release of Heavensward. Will it eventually need/want cross class abilities from Gladiator and War, most likely.

[Ghishlain]

Dark Knight uses gravity, slow and dark spells.

Do we know this for certain or is this just conjecture at this point based on previous iterations of Dark Knight in the Final Fantasy franchise? As far as I know, the only thing confirmed is that DRKs are (1) a tank (2) uses great swords and (3) has the power of Darkness according to:

[Verlyn]

I think it would be to their benefit to include the base game in the expansion and make people only have to do one purchase to get everything they need to start the game.
FFXIV 2.0 owes much of its success to its low cost of entry. They would be wise to keep that in mind going forward.