It turns out that Blake wasn't good at singing harmonies, which would be a capital-P problem on Glee. From what I understand from people who know more about singing than I do, all of the New Directions singers (and most of the other singers) have to be able to sing harmonies. Since there were two guys and four young women left as contestants, there was a same-sex female pairing in the homework assignment and in the video. Shanna and Aylin talked about how well they were going to do playing gay in the video, but didn't do that well according to the regular mentors. Apparently it's trickier than it would seem.
The female contestants seemed well aware that they could be playing lesbian characters should they make it to Glee. I don't believe it was planned on Glee that Santana should be a lesbian. It was established in episode 13 that Santana and Brittany had sex. Santana said, "Sex is not dating."
Brittany said, "If it were, Santana and I would be dating." Things developed from there until towards the end of the second season Santana self-identified as lesbian.
TV Tropes has the quote: "You may know me from Glee, which has been called the gayest show on television. You know, I’m sure they mean that in the best way possible." Naya Rivera
Apparently on the first season of the Glee Project, one of the contestants was shocked at the thought that he might have to kiss someone other than his real-life girlfriend, and quit the show over it. That's a big reason I've wondered a few times whether this year's contestants are aware that they could be playing gay characters, but I'm pretty sure now they wouldn't be terribly surprised if that were the case.
Shanna was the one who went home. I was surprised, as she seemed to be a favorite among the mentors. It's down to five contestants now. I'm not sure how they'll work it, but next episode is the semi-finals.