I brought musical numbers up in the thread mostly as a joke but I do think that we should incorporate music into the series to a greater degree.
The people at Disney are really good at doing effective and emotional musical numbers and this one is no exception, I think I can see what you're after. I'm not sure though that a singing Morgoth is going to work.
What I would like is more singing elves. Not just tra-la-la-lally elves and not just Maglor, Daeron, Lúthien, Fingon/Maedhros or Finrod... It should be a common feature that elves sing, especially during moments of passion or grief. I think of this scene:
Scenes like this can be very emotionally powerful and could potentially convey the tragic nature of the Silmarillion better than normal talking scenes. But I'm not really suggesting musical numbers, since the elves would really be singing out loud, not 'sing as a way to express things they are really just thinking or feeling inside'.