I really don't like Epic personally, but this is still pretty huge. Linux and SteamOS have come a long way. CEO Tim Sweeney has always been very negative towards the idea of Linux support, so Epic changing that stance would suggest that Linux/SteamOS has finally become too big of a market to ignore.
Who wants to bet that it will get to minimum viable product, be shoved out the door, and get basically no support until such time that Timmy goes "Well we aren't getting enough ROI on Linux" and bin the Linux version completely ignoring that they aren't even getting purchases on the windows client?