I do like the idea of it and it gives something for everyone to talk about. If anything I'd like to see it on the side bar with the hash tags under trending as thread of the day or something. At least to start out so there's more awareness about it and people interacting with it. I feel that would give more depth and meaning to many of the threads people are making and keep things fresh.
Perhaps one day would be random and announced such as a popular news, update etc that's happening. This would build community and awareness for now while the community is still on the smaller side of things and could be adjusted and changed after it grows.
This is a great idea, I had though of something similar but yours works better, I already wrote it in the ideas notepad and I'm definitely stealing it without giving any credit :P
But on a more serious note, there's also the idea of doing something like for Long form posts, so we can make noise in web2 by writing about current events and share those on Twitter and piggyback ride the hashtags, the only problem is that it requires speed from Lions to make the most out of trends. This idea is from @idiosyncratic
Nice for sure Articles still have a heavy weight in terms of the traction they can get from SEO and shouldn't be underestimated. Writing up a post on medium along with a host of other web2 article based sites that have a similar idea to what hive/leo is all about could make for some good traction. Also these articles if ranked would continue to drive traffic for a while