I don't care how you would redesign the DK class if you were a developer. The 3.1 patch notes thread is for discussion of 3.1 patch notes, not your giant wishlist.
I know that this thread is more about shoulda, woulda, coulda's, but I have been thinking about the changes that may or may not occur. Let me just throw my 2cents out there (which are never going to happen, like all these other theories):
First, the Death Knight should be totally based on DoTs and such. The strength of these DoTs should be effected by the 'tree' that the DK has been specced into. Second, each 'tree' should have their own DoT. Frost would have FF (applied by IT), Unholy would have BP (applied by PS), and Blood would have a blood varient DoT (applied by BB) (yes change BB to a DoT).
Initially these DoTs should have a minimal effect. There should be a couple ways to increase the strength of the DoTs. The first way to increase the DoT strength (how hard it hits per tick) should be the spec. A 17/0/54 unholy would have a very impressive BP disease applied. A 51/13/7 blood would have a higher blood disease applied. These of course would be because of the skill in each respective talent tree. A 51/13/7 would have a great blood disease but a sucky frost and unholy DoT.
Different abilities should amplify these ticks. Scourge Strike would increase the damage per tick for BP. Frost Strike would increase the damage per tick for FF. Heart Strike would be the Blood varient.
Another way to increase the strength of the ticks would be to make the DoTs stackable. This would probably be the easiest way to increase the strength of ticks.
Glyphs, enchants, and such are another way to increase the strength of the ticks, which is another easy way.
The first way is basically a total revamp of the DK class, which will never happen.
Another thing that I have heard people talking about on this thread that no body is talking about is CC. It seems that Blizzard has gotten away with this and intends on getting back to it. One way that would be very effective would be to have our perma ghoul go bye-bye, but in it's place have us have the ability to turn a monster into a ghoul (or undead) and control that npc for base amount of time. This controled npc would fight by our sides, like the ghoul does now. All of the CC that is in place now has the monster turn into something and just sit there picking his nose. If our controled CC ghoul actually fights for us that would be a very effective CC.
These are some of the ideas that I have in my mind.