Just finished watching all three episodes. Personally, I absolute love Amon. New favorite character. But I highly doubt:
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...he's Zuko. Zuko's story arc has already been dealt with, and it was beautiful. They can't bring him back just to deal with more inner self issues. He's already overcome all of that. Besides, he would be super old. I wondered if it might be Zuko's or Azula's son, but we shall see.
"It's not about the legacy you leave, it's about the life you live." ~Mara Jade Skywalker