The only real use I see for Impending Victory after testing a bit myself in raids/dungeons is only WHEN the healer goes down, which in a raid shouldn't be happening. So from my point of view, the talent is almost useless as I barely Devastate a target unless it's to refresh sunders. With an overflow of rage on raid bosses, Heroic Strike/Shield Slam/Revenge are my top priorities damage wise, + Rend ticks more than Devastate and by refreshing Rend with Thunderclap once every 15 seconds (with Blood and Thunder), means I can Shockwave for 10% more, which is higher than Devastate damage. (This is testing with 3 sunders. And for the purposes of my test, I wasn't testing threat values, purely damage on the Raiding Test Dummy. But again, Devastate is proving to be lower threat-wise than most of the above.)
My concern is that the argument you are giving is for threat, which is not an issue - I don't think anyone is contesting that point.
I have serious doubts that we will be sitting at full health on HM progression - even with all the healers alive. These bosses hit hard. Keep in mind that the impending victory buff lasts 20 seconds (maybe 25 with minor glyph?) So you devastate twice, and sit on the buff until you can get an effective heal out of it. Even in a fight where you don't cast the spell because you are not at risk - you would have gained ~3% damage output with those talents in a threat slot. With three points in War Academy - my average victory rush is hitting harder than my average revenge. I'm not convinced the threat trade off is as large as it is being presented, and if you are forced into a devastate/VR spam fest because of needed heals, who cares if you have a threat drop off?
I know the leading post in this thread says a 5% heal. But glyphed and spec'd these are hitting for 9.54%. These are not little heals. (included a couple SM's for a sense of relation)
I just don't think from an end-game progression perspective that you can ignore this for the sake of marginal threat gains.