In reality, if you end up in a situation when you can see that you won't have enough time to put in one more mutilate and then refresh SND in time using an envenom or eviscerate, I am guessing it's better to skip an extra mutilate and use a low combo point finisher to keep SND going. Is that right?

I see this becoming the same situation that Combat currently runs into.

Energy pool is low so the rogue activates Killing Spree or Adrenaline Rush to regain the energy pool.

For Mutilate builds, if your cycle starts to run into energy problems, pop Vanish for the Overkill bonus to help regain energy for your pool. This will help to, as Aldriana stated, "help to not get in that situation in the first place." Sadly, this is less helpful than either of the options that Combat has available for stabilizing a cycle, but at least it's something.

In addition to Vanish+Overkill, another somewhat handy thing Mutilate rogues can use is Thistle Tea, obviously not what it used to be, but it still does the job for the rare occasions where "you run out of energy to do all necessary moves before refreshing SnD". Though may not be able to get away with not having your healthstone ready for fights in Ulduar.

From what I'd been reading and seeing in the few 3.1 meters I've come across, combat was looking like the strongest tree. At the same time, I can't help but notice all the talk about Mutilate in 3.1.

Has Mut been showing stronger than Combat on ptr recently?

You have not been reading then. Mutilate for all intents and purposes is broken on the PTR. But speculation based on the patch notes of what they intend to do with it should boost it to and possibly above combat again.

Is there a reason we are suggesting kicking the SnD glyph instead of Rupture? It seems to me that if we're concerned about SnD dropping due to tight cycles, and the stigma behind Rupture is (presumably) "Keep it applied as often as possible," wouldn't it make more sense to glyph Mutilate, Hunger for Blood, and SnD?

The Rupture glyph, as I understand it, isn't a DPS increase so much as it is a DPE increase (as it only extends duration, not damage). The Hunger for Blood requirement should be a moot point if we're speaking purely in terms of a 25-man raid boss that will be subjected to Mangle, Deep Wounds, etc.

Indeed - I'm quite aware of that. But conversation is so exclusively focussed on mutilate lately, that it's as if everyone has already decided that it's the only way to go once 3.1 hits live servers.

Trying to figure out if I'd missed something along the way since I thought both were being considered viable specs on ptr ...

The Rupture Glyph does indeed add damage. If it merely extended the duration, there would be no reason whatsoever to get the glyph for raiding as, in the end, the damage would be identical.

This is exactly right. Most rogues swear by dual WD, the spreadsheet actually shows it as a small DPS decrease when you choose WD over SR for your offhand weapon. The significantly increased damage from SR compensates for the speed loss.

The Rupture glyph means you don't need to rupture as often, hence can spend more combo points on Envenoms; thus, it is a damage increase. Now, whether or not the SnD glyph actually adds DPS or not, it can be replaced with a point in Imp SnD should it be necessary; thus, the relevant comparison is the damage gained by Glyph of Rupture versus the damage gained by a point of Precision; and current estimates shows that Glyph of Rupture is worth more damage, and, as such, the usual assumption is that Glyph of SnD would be dropped.

The Snd glyph basically just offers you more pooling time. That is the only real dps increase it offers. You could say keeping SnD up is a dps increase but it is still possible to do so without this glyph.

Since one point into imp SnD already out does the glyph and we also now get the Mutilate glyph it really should not be that big of a issue to hold a rotation with one point into imp Snd. The only thing we need to make up for now is the 32 hit rating. (Forget the exact percent of HR=1%)