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.
Heroic is more than just an epic games launcher fyi, it's pretty much a full replacement for lutris (which I have stopped using due to the llm code shitshow)