[Formendacil]

It's not crazy exactly, nor a theory, per se, but as someone raised on the published Silmarillion, where Gil-galad is a Fingolfinian, I've always been somewhat dismayed that Tolkien's final thought on the subject made him Orodreth's son (and in the same text pushing Orodreth down a generation!) But the very same section of HoME XII provided a way out, had Tolkien but thought to take it.

Thus, my [completely illicit and unsupported] headcanon that Gil-galad was Arakano/Argon's son--Tolkien's single text about Fingolfin's youngest son says that Arakano (in Sindarin, Argon) perished just after crossing the Helcaraxë.

Gil-galad being his young son would have kept him a member of the House of Fingolfin, keeps him in Idril/Maeglin (and the late version of Orodreth/early version of Finduilas)'s generation. This makes the association with Fingon make sense in the context of Fingon's perduring bachelorhood (he could well have been fostered by his eldest uncle until his coming of age), and completely allows the retention of the idea that he might have been sent away to Círdan at the Havens, which never made as much sense to me as a prince of Nargothrond as it does a prince of Hithlum--making him the son of Orodreth seemed to imply Gil-galad's First Age history needed a rewrite.

This MIGHT make him a touch older than the implications--though no older than his first cousin, Idril, who was also a child during the Helcaraxë. If he's a bit younger than her (maybe conceived on the shores of Middle-earth days before his father perished), then his coming into prominence around the time of the Fall of Gondolin doesn't jar much with Idril's prominence really coming in the short time before that.

And there are other reasons he could have been sent away than simple youth! Perhaps his mother had a premonition (those are always popular) or perhaps he was sent to escort his mother to Círdan and then it was never safe to return.

But, again--complete fanfiction. Other than his (BRIEF!) dalliance with the idea that Gil-galad was Fingon's son, which CT thinks he was mistaken to incorporate into the published Silm, JRRT generally associated him with the Finarfinians. I just like my headcanon better.