Several Internet-only sites are already members of the White House Press Corps, including hyper-conservative sites like Newsmax and the Daily Caller. Breitbart could have a seat in the briefing room if it wanted, and can certainly afford to do so.
Well Steve Bannon already works for the White House, so Breitbart can have a seat already. I'm guessing less credible "fake-ish news" news sources that paint the administration in a positive light (but don't have press credentials) will have those seats.
My first thought was that they were trying to get around those pesky fact checking media and serve "The Message" directly to the masses.