But a few have remarked to me that looking more closely the hand/arm look too small to be Hamill's (it looks like a woman... THAT could be Carrie Fisher), while what you suggested was a shot of Leia I rather think is a shot of the young female lead receiving the lightsaber.
It could make sense.. .Leia got post ROTJ a lightsaber from Luke which she never trained with/used, but as she suddenly senses the Force in her daughter and sends her to find the reclusive Luke to convince him to train her/return to Leia because the force is "awakening", she gives her the lightsaber That would be very SW... if the lead/jedi trainee character is the girl, then the "quest giver" figure (ie: the Ben character, if you wish) needs to be her mother or a mother figure, sending her to "Yoda" (Luke). This would also be a replay of ANH to an extent, with Leia sending someone on a mission, with R2.
It wouldn't be too mythological for that figure to be a man, for a girl hero. It would also make sense for Lucas to have toyed with the idea of a female lead for the last trilogy, as the Hero's journey and its archetypes are different for women, and unlike the male ones with the OT/PT, he had not exhausted them yet with Leia and Padmé.
Plausible. But, if as you say "Leia got post ROTJ a lightsaber from Luke which she never trained with/used" why would she have a mechanical hand? Loss of limbs seems to generally occur in the SW universe during lightsaber combat. Also, is it likely that another Skywalker member loses their right hand? (As I type that question, I think the answer is that's it wouldn't be out of the realm of possibility.)
I just think that with the voice-over speaking about Anakin as they show Vader's mask, it makes sense that as Luke is talking about himself the scene would show himself, and the same with Leia.