Why Drop Death Runes?
Given the current state of the patch notes and preliminary number crunching, it's almost a given that you'll see most Unholy Death Knights drop Reaping come patch. Right now, everything suggests that it's going to be the smart thing to do. Scourge Strike is losing damage all around, and not only is Blood Strike gaining damage, but Desolation, the new Desecration offshoot, will provide its 5% damage boost from Blood Strike, giving even more incentive to drop those Reaping points, since you'll probably be wanting to hit Blood Strike to keep that buff up.
Here's another reason to use Blood Strike over Scourge Strike: Armor Penetration. One of the advantages of Scourge Strike in the early game is that it uses shadow damage, which bypasses armor completely. However, in return, it has a lower gross damage than similar physical damage attacks. It also does not scale with armor penetration at all.
Through Ulduar and now into the Argent Coliseum, Armor Penetration has only been climbing. It's looking more and more likely that tier 9 may be the point at which Obliterate actually climbs above Scourge Strike in damage for a well equipped Death Knight. Blood Strike is also physical, so that's, of course, one more reason to drop reaping and use those two blood runes for two Blood Strikes every single time for single-target DPS.
Now, Frost is less likely to drop Blood of the North altogether if only because it has that extra Blood and Frost Strike damage tacked on, so we may still, in theory, see some "use" of Death Runes. But again, chances are that when those blood runes refresh into Death Runes, they'll be converted right back into Blood Strikes. Frost has traditionally worked at firing off as many Icy Touches as possible, since between various frost damage increasing talents, and Icy Touch dependent proc mechanisms, it just did the most damage. Plus, the Icy Touch glyph allowed for more uses of Frost Strike.
While the latter point still stands for now, the various nerfs and changes to the Frost Tree are now suggesting that a simple rotation may now work the best for Icy Touch. Blood Fever's damage boost may finally make it worth using in a rotation, and as a result, Obliterate and Blood Strike will finally outpace Icy Touch more solidly.
What it means
It means, for one, that things are going to get a lot simpler should these changes remain exactly in place in future PTR builds. You can probably expect, for Frost, to see a very basic Plague Strike -> Icy Touch -> Obliterate -> Double Blood Strike rotation come into effect. Unholy will be similar, but replace Obliterate with Scourge Strike until Armor Penetration gets high enough. It's possible, of course, that more testing could change how we see these changes, but for now, the math really does appear solid: For the Frost and Unholy trees, Death Runes are on the out.
Right now, it would definitely be interesting to hear what Ghostcrawler has to say about the Patch 3.2 changes in light of his comments. The Death Knight Q&A seems to have been conducted before Patch 3.2 was pushed onto the PTR, so It's certainly possible that, in the meantime, he and his team looked at how to adjust Death Knights and decided that they had to sacrifice Death Runes for Unholy and Frost Death Knights.
But this does simply make single-target DPS rotations straight up far less complicated. You'll still have some variety in Frost in trying to make proper use of Killing Machine and Rime procs, but otherwise spending your runes will be a very straightforward proposition.
Unholy's biggest interesting conundrum is going to be trying to figure out if or when one should give up on Scourge Strike and head for Obliterate. In theory, a high level Unholy Build will still have those 10 points in Frost, and one can use the 3 talent points saved out of reaping to grab Annihilation, so you shouldn't have to worry about the disease-eating portion of the skill.
What Changes May Come
Of course, this is the PTR, so things are liable to change, maybe even drastically. What might change, exactly, is more up in the air. As I said, if the dev team doesn't mind deemphasizing Death Runes for 2 of the 3 trees, it may be these changes as they stand may make it to live servers with minimal adjustments. If they do want to at least make Death Runes a viable option for Unholy, they may add some secondary benefit to Reaping like they did to Blood of the North.
Of course, the Scourge Strike scaling issue will probably need to be dealt with, by Patch 3.3 if not Patch 3.2. While a removal of the current nerf might help, in theory, it would also not solve the underlying problem of scaling, so it may be that the weapon damage may need to be bumped slightly, or the extra shadow damage given a percentage modifier or a high AP/"Spellpower" damage coefficient, in order to add some more scaling to the strike itself.
Whatever they do brew up, it's probably more than likely that Death Knight changes aren't quite done on the PTR. Hopefully, we get a more stable build and a functional Argent Coliseum raid soon so we can really put the new talents through their paces. In the meantime, keep on trucking, Death Knights, and enjoy that AE Unholy Blight while you still can.