In the 43rd millenium the Universe is k-k-clean and the Eldar live happily.. alone.

Sorry to burst your bubble, but http://wh40k.lexicanum.com/wiki/Doom_of_Malan'tai#.Um4Nq_lwqXw this guy kinda spoiled that ending.

Yay! No more Grimdark! =D

Speaking of another UNLIKELY scenario .

But that's not actually that unlikely. It has been seen by every major Eldar Seer that it WILL be born.

Will it give the Eldar a chance to return everything to like it once was? Most likely, no. Will it deal with Slaanesh and free the Eldar of their curse, thus giving them a much better chance of taking back their lost Empire? Yes. That, and having a pissed-off god at your side DOES give you an edge.

You have a much bigger threat to deal with.

Get rid of Slaanesh? Nah but I agree that they could bring their god back, although the Seers see the future yet the future is always in motion so I wouldn't rely on those visions too much.

Ynnead's whole point is to subdue Slaanesh so that the Eldar are free of his/her (its?) thirst. Whether or not that will come to pass is anyone's guess, but I'm not exactly sure what the Eldar's game plan is after that, considering that Ynnead will only show up after every Eldar is dead and their souls contained in the Infinity Circuits.

Let's celebrate with gathering here to play RP: In case you are interested in some RP: http://forum.eternalcrusade.com/threads/tides-of-destiny-wh40k-fiction-rp-voting.1679

Regards the 43k stuff..... Most likely the Great Devourer will get rid of everything and it will end in a Tyranid vs. Necron war and the Eldar retreat into an other galaxy, while the other races most likely die, desperately trying to hold on their territory.

I might kick in here that what we have seen of the Hive Fleets this far (Leviathan, Gorgon, Behemoth, etc.) are ONLY SCOUT FLEETS!

That is only ONE theory of how Ynnead might be born, mind you.