Subpackages
See openmw-mods#366 (comment 959108706)
Packages which are logical subunits of existing packages. This lets subcomponents be versioned. Subcomponents could include: optional features packaged and versioned separately and patches for long-dead mods.
It might be possible to also use this for multiple variants of the same mod, however switching between the root package being a virtual and not would be messy (though epoch versions would help), so it's probably better to stick with regular virtuals.