The game is a 3D RPG for the Wii U — presumably the eShop. The title comes from the fact that the game is set at the conclusion of the year 1999.
Here's some of what has been posted on the official blog:
Two Brothers is still our main project. We began Project Y2K before we started Two Brothers and put it on hold to finish Two Brothers, as it was a smaller project.
Everyone who has completed work on Two Brothers is now working on Project Y2K… so that’s about a third of the AckkStudios Team.
Now that Two Brothers is nearing completion, we felt it was time to return to Project Y2K. Project Y2K currently exists in a few forms… concept art, a finalized script/story line, a completed graphics/gameplay engine.
As for the title Project Y2K, we can tell you that the reason we’ve chosen this project name is because the game will begin January 1st 1999 at 12:02 AM…
It certainly sounds like it could be an amazing concept - hopefully we'll hear a bit more about it via the blog itself.
Thanks to Emily Rogers for the tip.