I can't imagine a lot of those first 52 monthlies are going to last very long, and I don't think DC believes they will either. Seems to me to be a throw everything including the kitchen sink out there and see what sticks approach.
Which means at some point, they'll need replacement monthlies. I'm hoping that Power Girl is one of them. She was trending up in sales again in May, after a small downturn the previous month, so maybe there's hope. And her merchandising seems to sell quite well.
Honestly, if Penguin can get a mini, PG should be able to score another monthly, this time hopefully with enough name talent behind it, and enough stories that matter to the larger DCU that it attracts a much more sizable readership.