Looks like work on the Aquarion sequel is still progressing:
(stolen from the official Aquarion blog)
The subtitle is "Uragiri no Tsubasa", or "Wings of Betrayal" (as I think the English text says on the picture); while it LOOKS like Apollo and Silvia, the subtitle would suggest it was more likely to be a Apollonius/Celiane story. Guess we'll just have to wait and see!