There's probably nothing as of yet. Look at some facts:
- ED is starved for content, and the Frontier knows it. They're not fools. You can only shoot ships for big money, dock ships for big money, scan balls for some money, or mine asteroids.
- If there is some playable feature-complete content out there, they would have announced it already.
- An actual alien race or whatever would take loads of time and effort.
- If they drip-feed news to the starving masses, it builds hype and keeps people from leaving.
- They can use this to buy time to develop 2spooky4me aliens or whatever it is they're planning, and they can even get ideas from what the community is speculating about.
I agree with all these points. I can't imagine they spent lots of time developing alien ships and technology, then hid them in a game with 400 billion systems (maybe 1 trillion planets?) and hoped someone would eventually find them.
I think this is the "hype" phase. Maybe the artefact is all there is for now; but I'd guess there are a few more steps/clues coming. At the end of which is likely some kind of warning, a shipwreck, a destroyed station (how cool would it be to explore a dead, darkened station from the inside?). A warning message. But no aliens, yet.
If Frontier are clever, they'll interweave their story with the player-generated theories. Someone comes up with a really clever theory? "Oh, that's good. Let's hide the next clue there, and we'll pretend it was there all along". Keep us all engaged.
The aliens will come in a future update - maybe soon. The Galnet hints and the introduction of a combat-explorer seem to point that way. That said, with Powerplay on the way -who cares about Galactic politics when aliens are banging on our door.