This functionality would be very, very welcome.
Our existing (single-module) overlays are shipping as regular standalone dylib targets (not frameworks). Discovery is done through a naming scheme, with no requirement for explicit registration. Is there a specific reason to define these cross-cutting overlays as full frameworks, or was that just a non-normative example? (Our existing single-module overlays are standalone dylibs, not frameworks.)
+1. I think we should have a strictly enforced naming scheme for such overlay modules.
Followup: why not just do away with JSON descriptors entirely, and figure out what cross-cutting overlays need to be loaded based on their name/location, like we do for regular overlays? (There is a combinatorial explosion, but only if we don't have a complete list of all such overlays. Admittedly I have no idea if building such a list is feasible.)