I didn't catch the change. Someone else pointed it out in an earlier post. But they also pointed it the stars are still there. It's not totally dark. But it does ruffle me since WR was known for changing its ED as it neared the end, and in WR things did get gradually more sinister.

You bring up a lot of good possibilities for what could have been going through Suzaku's head. Maybe the creators just wanted to leave it up to us this time. I would call them lazy, but again they were deliberate in those scenes.