Well, to be fair, many of his predictions did come true. It is possible we are waiting for everything to play out. All prophecies are open to interpretation, and here is mine over the skies opening wide:
The heavens in fact do part, because not only does the sky open up (giant gaping hole, you know the one I'm talking about) right above the Temple of Sacred Ashes. The final resting place of Andraste.
As far as the "he" goes, I would say that it could be referring to Fen'Harel. Once he awakens, everyone will know.
Yeah but why would he say heavens and skies if those meant the same thing? Usually heavens refers to Heaven, or space. It can apply to the skies as well, but in that case why mention skies as well? It implies he was referring to separate things.
The skies opening wide could be the skies of Orlais and Ferelden. The breach occurs perhaps between them.
I'm not sold on Fen'Harel though. When he rises, everyone will see. We haven't seen him yet as far as our characters are concerned. In the game, we see him as Solas. It isn't until the end that we the players see him as Fen'Harel. So maybe the next game is about him rising, but at the beginning of Inquisition's events he was weak when he arose.