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 lets you log in with your GOG, Epic, and Amazon accounts and install/update your games like Steam. If all your games are on Steam then it's pointless, but if you have a GOG library, it's quite convenient, and it will automatically set your games up with your Proton variant of choice.