But I wasn’t asking about file sync… I don’t think I can be any clearer than I already was when I said SyncToCloud looks exactly like the kind of thing about which I asked whether it already exists. A database that knows where the saves are stored and automates the rest for you, that would be regularly updated through user contributions.
Huh? ScummVM savegames very much work across platforms. And yes, they’re game specific, but that’s kind of the point, isn’t it? 
Did you get confused with Steam or something?
No, not at all. On a more modern game you might be able to set that up with relative ease, especially on platforms with easy symbolic linking, but you can’t just put a program that expects executable, config and saves in the same directory on Dropbox/Syncthing because of the differing config. Monkey 4 does happen to use an Escape from Monkey Island/Saves subdirectory, so that would be a simple one to sync. Of course you need to find it first. You start in the game dir, move on to the likes of AppData and My Documents, maybe UserData? Local Settings? Where’s the stupid savegame hiding?! C:\Users\frans\Saved Games? No, that’s some Darksiders thing… Ah, found it. C:/Users/frans/AppData/LocalLow/Microids/Syberia3/. Oh, and great. It includes the options. So it’s still worthless for simple sync even after spending a couple of minutes to find it.
Another example of the same format is Hocus Pocus. It stores saves and config in the same directory, with the game. So how could it possibly be that I don’t want the same config on a game that old, as opposed to Syberia 3? Well, my desktop has a gamepad and my laptop does not. Also, even though old games are typically on the smaller side that still doesn’t mean I necessarily want hundreds of megabytes in my sync folders.
These aren’t hugely complex problems, but it’s a far cry from “just use generic cloud sync.” It requires starting the game, figuring out where it’s created the save, setting up all kind of stuff, and that on every single one of the platforms where you might want to run it.
The GOG Galaxy process for Monkey 4, by contrast, is two clicks. One click on install on the one system, and a second click on install on the other. You won’t be able to make it quite that simple with a generic solution, but you might be able to make it just two or three if you wanted to and the means exists. One for install, one for generic specialized sync.