It's good to see someone so enthusiastic about Dark Knight! Still, a couple of things you should know...

First, as a new poster here's a trick you can do to avoid having to post multiple posts in a row. If you're going to write a long post, write it in a notepad and then post only the first paragraph. Then, edit your post, and copy the rest of of your post into the edit window and repost it. This will get around the 1000 character limit and allow you to place your entire text into one post. It's what I did with this very post, which is 1913 characters long.

Secondly, a Sward is not a Sword. A sward is a grassy stretch of land, not a bladed weapon. Heavensward doesn't refer to a weapon. It probably doesn't even refer to a grassy stretch of land - they probably mean Heavensward to mean "in the direction of the heavens" or "toward the heavens". The idea of DRK using a special sword is a good one, though, and very much in-keeping with the lore of Dark Knights in some of the prior Final Fantasies, such as Cecil's dark swords in IV, and the Deathbringer granted to you by Zeid in FFXI.

I think that making Paladin and Dark Knight mutually exclusive will be a tough sell. Folks already whine loudly about having to choose which way to distribute points when playing Scholar and Summoner; I can scarcely imagine what the backlash would be like if everyone who has leveled Paladin would have to throw all that away just to play Dark Knight!

Lastly, I wouldn't be too concerned about DRK-bandwagoning making it tough to queue. The fact that it is a tanking job is going to scare a LOT of people away from playing it! While it may spark enough interest that many players who normally don't want to tank will try it out anyway, I very much doubt that there will be enough such people that we actually wind up with more tanks than can be supported by the groups seeking parties in the party finder.