Some interesting industry news for you here. Epic Games have announced a change to the revenue model of the Epic Games Store, as they try to pull in more developers and more gamers to actually purchase things.
For generic SteamWorks integration, there already exists a open source DLL called Goldberg Emulator. If publishers opt for real DRM, the games are not available on GOG anyway.
Also, downloading and backing up the games have to be done by yourself before the storefront goes bust. Distributing GOG games outside of GOG is a copyright violation, unless the copyright holders explicitly allow it.
So, to sum up: You can backup DRM-free Steam games and make them work with little effort.
Until it doesnt and your entire game library is done…
For generic SteamWorks integration, there already exists a open source DLL called Goldberg Emulator. If publishers opt for real DRM, the games are not available on GOG anyway.
Also, downloading and backing up the games have to be done by yourself before the storefront goes bust. Distributing GOG games outside of GOG is a copyright violation, unless the copyright holders explicitly allow it.
So, to sum up: You can backup DRM-free Steam games and make them work with little effort.