Oh my god, after your last thread I was thinking about that :D I've seen many speculations, i'll try to do a résumé here.
There was a theory that Solas might be Shartan, the elven leader of the rebellion with Andraste. He is often represented bald, as is his in-game spirit model in DAO. His tarot card is very, VERY similar to shartan's stained glass representation (There's one in redcliffe) Some of his representations are with human-like ears, or a hood that hides them, because the Chantry was like eww elves ew much unworthyness or something. (You can learn more with Geekremix's video, "A love forgotten". And all of their videos. They're awesome.)
Another theory states that Solas took Felassan's body, the elf from the Masked empire book, supposedly to not be recognized as Fen'harel. BUT during the Wicked hearts, wicked ears quest, Briala was there, and briala knew Felassan personnaly. It might explain why Solas shaved his hair, to be less recognizable, AND had that horrible mask. In the art book, that one mask was supposed to hide a good part of his face. There is also further speculations stating that he removed Felassan's vallaslin off his new body, and changed his eye color. (Magic is known to do that.) You can learn more with girltriesgames's youtube video about the subject. IMO that's crazy, and it would mean that all of us solasmancers were heads over heels for Felassan. Or his body ? Damn, that's super dark. ALSO : Solas has a jaw bone as necklace. Felassan's name means "slow arrow." Solas killed Felassan at the end of the Masked empire, confirmed by one of Cole's banter in Trespasser : "His friend had to die, because he thought they were people. A slow arrow breaks in the sad wolf's jaw."
I think all of these theories are very interesting ; It's possible none of this is true, it's possible all of it is, and I personnaly think that it's a mix. :) ")