Maybe not a merge, but "multi-reddit" type experience where you can subscribe to the multi-feed for a genre of communities and then unsubscribe from ones you don't want. Like, a gaming multi that would have all the top-level c/gaming, and things like gaming news communities, or multis based on all nintendo related communities or ps4 related or whatever.
Like if there could be a tag system where mods can tag their subreddits main theme (maybe from a list populated by matching, like "nintendo' and "Nintendo Games" would correct to "Nintendo" like what I have seen on LinkedIn for selecting job industries when you put in "marketing" it corrects it to "Advertising Services" or something. Then the tag would be the multi-community hub.