According to the official brochure, episode 5 of Mobile Suit Gundam Unicorn
will be released in May 2012. The title is "Black Unicorn".
According to Famitsu.com, the original author Fukui Harutoshi
announced at the premiere stage event that "I know everyone is worrying if we can wrap up the story with the final sixth episode, but I have come up with an idea. It will be revealed in the next episode."
Sources: Scan of the announcement