As far as we are concerned, out-of-tree modules do not exist. The module interface is only for in-tree users, which are fully supported. GNOME takes the position, or at least apologists like you, that out-of-tree GNOME extensions are a good thing. As far as Kernel developers are concerned, out-of-tree modules are never an answer. Device drivers should live in the kernel. Period. If Nvidia chooses to do otherwise, that's their problem. But we didn't kick Nvidia out of the kernel.
GNOME kicked 2-d workspaces out of the core DE, because they didn't want to support it. They think that they want to keep things "simple" for their users. Google "GNOME Feature Removal" and look at the history. They took perfectly working features and ejected them from GNOME. We don't do that in the kernel, unless we are sure there are no users. And if we are wrong, and people complain, we'll put the feature or architecture support back.