This has probably been suggested but how about getting rid of BL and CL and creating a semi upped league? Up to 1/5 of your deck can be upped cards or something like that.
You would get double the cards to work with, there would be less optimized decks to copypasta from the forum, and the metagame wouldn't be fully figured out yet so it might bring some freshness to, from what I gather from the posts around here, a stale game.
I think the broadest part of the community is people like myself with a number of good upped cards but enough enough to build full decks covering the full spectrum of archetypes needed for CL. Obviously newer players would be excluded and a completely unupped league would probably still be needed, but I don't think it's completely unthinkable to imagine someone doing well completely unupped. Unifying the leagues also helps the small player pool problem.
I don't have much experience with this community or either league, but just from lurking in chat and reading the last few pages it looks like CL isn't really working.