I wouldn't necessarily put that first condition as being absolute. Much of it has to do with playing a rogue intelligently rather than requiring only druid/pally tanks and/or specialized encounters.
I presently run with ImpXA Mutilate using a warrior as our primary tank in Sunwell. He's an aggro beast, which certainly helps, but I also don't do unwise things like open with mut > mut > 5cp ImpXA; effectively locking out a healthy chunk of his initial threat generation.
If you open with a normal DPS sequence (getting SnD rolling and 5cp built up) it will "generally" allow the warrior to get plenty of threat off the start. If you really burst the CP's, drop on a rupture first and cycle in ImpXA at the second cycle. Same thing if you notice that he hasn't built rage or missed shield slams. It lets the warrior get 4-5 Sunder/Devastates up, after which, they only lose the threat generation of the sunder effect itself.
My general cycle uses SnD > ImpXA > Rupture. I can almost always keep all three active, and only the rupture requires coordinating my timing to have AtoL and FW up. Mutilates fit nicely into a three finisher very easily.
The DPS difference with ImpXA is around 4.35% for ALL physical DPS classes (including your tanks getting additional threat by hitting harder). On some of our Brutallus fights, I've loosely calculated this to be 600 additional DPS for the raid. Under normal raid buff conditions, it ends up being closer to 350-400. This is more than I would benefit the raid if I had dual glaives. And yes, my DPS _is_ lower than full combat rogues by roughly 5%. But really, they're one of the reasons that I'm putting ImpXA up in the first place...
So I'd amend the rules to be more along the lines of "communicate with your warrior tank if you're going to use ImpXA. Make sure that he's comfortable with the change to threat and practice on a few mobs before trying on bosses."
