The problem with CIG's approach they have to spend a lot of effort in adding things to the engine that game engine makers do for other developers who license their products from game engine makers and let the game engine makers worry about that side of things. They of course, pay for this privilege.
"StarEngine" is probably so customized at this point, they probably can't accept updates from Amazon any more, it would probably break CIG's engine.
I'm not saying this approach can't work. But it does require a lot of effort if you have any sort of complex game, and want to do even more complex things with it, and i hope even LA won't deny, CIG want to do some really crazy and complex things with their engine.
But perhaps this brings us around to the real issue. Custom engine, Unreal, CryEngine, whatever. It really doesn't matter, because they would still have to implement a lot of what they want to do themselves, unless the game engine developer also adds those things natively to the engine.
And all these discussions do highlight the fact that CIG still have a boatload of work they need to do on the engine anyway, and anyone dreaming that SC (and maybe SQ42) is being released in current_year+2 is probably dreaming.