One idea I always enjoy which answers the question of what happened to Maglor after the First Age involves him getting entangled with Sauron. What are the circumstances in which he ends up in Mordor? Was he imprisoned and tormented, left to live his life in regret while locked away in Barad-Dûr or has he been brainwashed to serve Sauron faithfully?

What would Sauron even need from Maglor? A chance to humiliate the House of Fëanor further? Perhaps he lusts after Maglor's voice? Or he needs Maglor to help him build something.

Did Maglor survive the War of the Ring? Did someone find and rescue him? And if so, in what condition was Maglor in?