Don't worry, my Dunmer DK can share this duty with yours.
I don't want to come off as being dismissive, but I do feel that you may be over generalizing. I sincerely doubt there is much to worry about. People will ultimately play what they want and what entertains them. I'm sure there will be plenty of DK's shortly after launch.
I hope you find something you like and enjoy the game. I'm really looking forward to this. I'll be shedding blood for the Pact, so I'll see you on the battlefield!
Vert
Right after I create a Khajiit Sorcerer, I'm making a Khajiit Dragonknight. Not even remotely interested in playing a Nightblade. And yes, I will be in the Aldmeri Dominion.
Sorc class can be one of the best tanks there is. Lulz.
You do not need to be a DK to tank. Any class can tank so get out of the thinking you need to be a certain class to do a job.
A sorcerer can tank just as well as a dragon knight or nightblade. It all depends on equipment used.