I realize Zeid could do that, I'm not really poking fun of the OP or anything really (I'm sorry if it came out wrong).

Only couple of Dark Knights comes to mind when they could summon something like shadows, Zeid being one of them.
Other career Dark Knights in the FF universe couldn't though, to quote Cecil or Gafgarion for example.

While it's completely plausible the idea, DRK is a job that fits the role of "front damage dealer". It's iconic that they can cast dark magic and have all that dark aura around them.
When you put that into a MMO, you see, every job has a role. Some will fit the same role as a "front damage dealer", but there are things called "spotlight".

It's of Dragoon's, Summoner's and Beastmaters spotlight to get aid from a third-party. That was iconic, through out FF history. No exceptions on XI (maybe not DRG, I haven't seen a Lancer summoning a wyvern at all).

However for Dark Knight the emphasys is another: It's ... cast those spells and slay those mobs. Don't base yourself based on what one or two dark knights can do (btw, Ark Angel TT couldn't summon anything, same for the "necromancer" who's just a Dark Knight in the Drachen Armet fight if you've done it). There's a whole history behind all of those jobs. And through out such history, no Dark Knight was able to summon anything.

Dark knight summoning a companion is a "new thing" that only happened in XI.
I might be wrong, but I doubt SE would implement such thing.



However, it is a nice sugestion that I wouldn't mind being applied really.