The current DK mechanics aren't really that hard for boxing.

A rune refreshes roughly 5 seconds after you use it.
If you're in Unholy presence, then abilities have a 1 second GCD.
Other presences they have a 1.5 second GCD.
And you'll occasionally do Runic Power dumps, also on a GCD.

Ideally, use all your runes, as a 1 Frost + 1 Unholy will hit harder than a single rune ability.

Probably four moves that use runes, with a total of six runes to be used.
Try to have the Frost and Plague diseases up all the time.

Then use Death Coil as your runic power dump.

Also have the ability that spreads diseases as a hotkey.
Could put it into your rotation if you like; single targets will die fast irregardless, so it won't hurt.