Wait, are you sure?
I thought that the Akaviri beings were dragons, and that they disappeared from Tamriel for a while, which would explain why the Elder Scrolls prophesied their return...
Nope. The Skyrim forum is part of the demesne of Lord Sheogorath, and their patron-saint is Malkav. You must be wary of what comes from its residents. So, let's explain some TES V politics, and you will see the true origin of the Akaviri stuff you've been hearing.
Way back in the way back machine, there was a time before Fallout 3. We had, through the divination of publicly available information on Copyright and Trademarks, discovered that gamesas had copyrighted the word Skyrim. Naturally, this prophecy of the future was never fully circulated across all human channels, so only a middling amount of the forum remembers this secret. Thus it was forever debated whether TES V would be in Skyrim, Summerset Isles, Valenwood, what have you. Now, I see your confused look on your face, through your CAT 5, and I can tell your wondering what this has to do with anything.
You see, one of the most commonly suggested plots for TES V, even in the days prior to us divining the secret of Skyrim, was an invasion of Tamriel by Akavir. It would keep getting suggested, over and over again, month by month, week by week. It was still getting suggested right before the Skyrim Teaser trailer. And then, BOOM! We had divined correctly TES V's locale as Skyrim, and not only that, it was going to feature a civil war in Skyrim and Dragons attacking.
The scholars of our forum, deep within their libraries and heads full of references, made the connection that Alduin, the World-eater of the Nord Pantheon, must be the antagonist and the dragons are his servitors. Of course, our dear scholars were right, for they had already received the gifts of MK, the guy who writes a lot of gamesas's weirdest lore books. These gifts, in the form of the seven fights of the Aldugadda (or however you spell it, it features Alduin prominently), and other texts, gave them enough clues to correctly predict Alduin's involvement.
Of course, the libraries of the lore forum are rarely visited, even though they are public. (Their publicity is terrible, half the people here probably don't know this forum exists) So the general public continued their attempts at advancing their favorite theory, the invasion of Tamriel by the Akavir. Grasping on the book, Mysterious Akavir, they twisted an already sketchy text high and beyond, to dark corners of weirdness and confusion. The idea of Akavir invading Tamriel was twisted into a macabre story of tiger dragons and lunacy, and thus, the forum's oldest prediction of TES V's plot was made to fit the Skyrim trailers.