You realise this is provable just as much as anything on WoL, right?
Ele shamans are a stackable class on heroic Durumu, for example. Go to wowprogress and look at the first guilds to kill that boss. I've already provided some examples - Blood Legion, world first on that boss, used two, one of which was an alt and still finished top 5 on the meter, and Method, world second, used three, and again one was an alt. Next, go to youtube, search for the name of the guild and Durumu. Find their kill video, and watch it. How many ele shamans do they have? Is it at least 2? Try another guild and repeat. Or you could just take my word for it. But if you don't want to take my word for it that's totally fine, you can check for yourself. Raidbots is not the only valid resource in the world, and it's not "hearsay" to find information somewhere other than a collection of WoL data.
I don't know when you'll run into the first guild that doesn't have ele shamans, but I can assure it won't be anywhere near the top.
This = Logic
Are they stacking elemental for other heroic fights? The only one I've heard of is Heroic Durumu.