I just posted this on the wowhead dk class forums today:

"Just had a thought. What if you have a level 55+ character and you create a death knight. Later you transfer that primary 55+ character to another account. Would the death knight on the first account still be playable? Would you be able to create another death knight on the 2nd account now? Something to chew on."

Makes me think, since I'm getting my new computer before the xpac comes out and I want to move up to 5 boxing, wouldn't it be easiest to add 3-5 new DK's? All I'd have to do would be create 2 new DK's on my existing accounts, then transfer my two level 70's to 2 new accounts to create 2 more dk's, then wait a few days, transfer 1 level 70 again, and bam! DKx5 at 55. Not a cheap solution by any means, considering I'm already paying for a new computer, adding 1-3 more accounts, upgrading to both expansions on all accounts. But hey, it's possible.