Yoshi and the Mysterious Book will sell for $60 in the eShop and will have an MSRP of $70 for the physical cartridge.
An opmist would say that it is $70 game and they are adding a $10 discount for buying it digitally. A pessimist would say that it is a $60 game and there is a $10 fee for the plastic cartridge.
I am not sure if you can do it on a Switch, but I recall the 3DS having a feature where you could pull patches and DLC from one console to another. Not even close to what you were suggesting, but it is something.
Do any software stores support creating a local package mirror? I suppose you can make one for GoG by periodically checking for new game versions and saving the installer to a backup.
Not just the installers, but plenty of games (all of GOG’s catalog, but also a bunch on Steam) don’t have DRM at all. They’ll work just fine if you run the executable file without the “store” running (even if you got the exe file from Steam/etc and can’t re-download without a login thus functional servers and account in good standing and internet connection).