A certain pally discord has been discussing it a lot. Apparently the old “spamstring/wingclip” trick doesn’t work as well as thought, because of how on-demand yellow attacks are batched in a weird way, nullifying whatever uptime gain they’d otherwise(a very broad way to put it, but that’s how I understood it.) Apparently, it actually worsens uptime.
General overall conclusion is that nightfall has a base 1ppm, and from a pally PoV, proc chance can be doubled via SoR, giving an average uptime of around 20% at about 1,000 swings. About 18% with SoC. (The following aren’t my logs.)
https://classic.warcraftlogs.com/reports/VWCKNqP4LBYzXGmD#fight=last&hostility=1&type=auras&source=1&spells=debuffs
https://classic.warcraftlogs.com/reports/ZnWJkjPThD74YQBg#fight=last&type=auras&hostility=1&source=1&spells=debuffs
The consensus is that it currently is not worth it; the damage gained from the debuff does not make up for the damage lost from hunter/warrior spam rotations, or pally sitting in SoR. You’d get more or equal overall raid damage from a pally with OEB playing as normal ret than having them wield nightfall. I imagine it’s similar for warrior OT’s and melee/melee-weaving hunters.
It will, however, be more valuable later as casters get more powerful. Think naxx with ignite mages and when warlocks finally have a nice heap of hit gear. At the moment? It really makes no difference, and may actually be worse off than just having the nightfall player focusing on personal DPS.
(Edit: accidentally stated base PPM as 2 instead of 1 - it should be 2, but it is not.)