mm324: Not a bad idea, I wonder why GOG doesn't do it?
F4LL0UT: Well, with some of the automation I can imagine it's both technical difficulties (maybe also security risks) and the other reasons I mentioned like the risk of installer versions receiving too little support. I guess with increased automation for the Galaxy versions the patch and DLC delays would shift from Galaxy versus Steam to GOG installers versus Galaxy. There's probably also a number of other variables at play that only GOG is aware of. Either way, the more I think about it the more I'm under the impression that many problems could be solved by redesigning the Galaxy API and (something I totally forgot about above) improving the documentation of the API. I've seen a number of developers complain about its lacking documentation by now.
As for the lack of native support for Galaxy in popular engines, I'm honestly under the impression that GOG just didn't even think of approaching their developers or at least half-assed this very much.
GOG is noticeably bad at attracting or retaining programmers in web and networking fields. It's really quite marked. Perhaps they don't pay enough to compete or perhaps it's not glamorous enough to work for GOG instead of other common employers in eastern Europe? Whatever the reason I simply doubt GOG has the technical skill to move quickly on Galaxy.
Also, I don't know how seriously most engines would take them if approached. GOG would probably have to offer to do a lot of the work themselves, and Galaxy is still in beta. I'd much rather GOG focused on getting Galaxy up and working, then started outreach efforts to get a functional product integrated into engines. Evangelizing beta product is risky when Steam is right there.