It seems like GOG clearly needs to include a clause in its publisher contracts that games released on GOG will be expected to receive adequate support and timely updates, or they will be removed from the store. Is this really so difficult?
As far as I know such clause already exists. However it is not much of use if GOG does not enforce it.
There is a simple solution for dealing with publishers leaving GOG users with outdated versions:
* GOG should mark the game as "Outdated" in their catalogue and on the game's product card;
* the game should go on permanent
sale (say 80-90%).
The second option would almost certainly require GOG to revise their publisher contract (if they haven't considered this already) but would also provide a significant commercial incentive to publishers to keep up-to-date, or risk losing significant future revenue.
Marking such games as "Outdated" would be a fair option imo. Of course nobody would buy it and maybe this would lead devs to update the game after all. However regarding the pricing that's not up to GOG so putting them on sale is no option.
GOG relies on support, rather than game providers relying on GOG.
Mostly talking big DEVs and PUBs here, as Indie games or small independents are a different story.
Make it to onerous at GOG and providers will just stick with where they make most of their sales - Steam.
This might be true for big publishers but I have spoken to several indie devs and they really WANT to be on GOG even though they are on Steam. If you ask me, I'd rather have more of those "I want to be on GOG and support it" indies than those "Well ... we could get some money on GOG as well ... we don't need to put much work in it and can abandon it sooner or later" big publishers - but I am sure that I am in the minority here since most GOGers prefer to have the big publishers and the big games here ... even if that means that support might stop whenever they want.