Equestria Daily is actually a blog that dedicates itself to MLP:FiM news and fandom interests. They heavily feature popular or exemplary art, music, and fan videos. It was one of the first news sites to pop up back in the early days of the shows popularity, and one of the two still active today. The other is Derpy News. The Daily Oat shut down about two weeks ago. Equestria Daily still owns the market share of site visitors though, especially after devouring most of Everfree Network's visitors after its shut down late last year.
This will actually be Equestria Daily's second "expansion" in the past few months. Back in January, they launched Desu Daily, and it's primarily staff by previous Equestria Daily writers who either weren't a part of the MLP fandom anymore, or who had taken more of a background role in updating the site's news. They didn't expect it to take off quite like Equestria Daily did, but mainly it was a place where MLP & anime fans could find news quickly without having to go to different dedicated news sites. They feature the same style of news updates and art posts as Equestria Daily, but for a different theme.
I expect about the same for whatever they call the new Steven Universe site. You'll probably see art posts, fan videos and edits, fanfiction if it becomes popular enough, and every little bite sized bit of show update on their blog. Equestria Daily tries to stay out of drama topics or controversy, so if any weird shit happens, expect it to be glided over or ignored altogether.
Tumblr's problem with it seems to be that it's run by "Ew, Bronies". Thing is, most of the people who will be writing for it aren't really into MLP:FiM anymore, so their vitriol spewing doesn't have much merit. It's Tumblr though; facts don't matter when feelings are hurt.