What is the meaning of "Cross" in the title Cross Ange?
The original explanation in Japanese in the preview cited in the question is


  「アンジュが苦労｛くろう｝する」ってことでしょう？


which roughly translates to


  Ange has been through many hardships, I guess?


In Japanese, the pun is on Cross - クロス (kurosu) and 苦労｛くろう｝する (kurou suru).

As of the time of writing, this is the most official explanation on the meaning of "Cross" in Cross Ange.