In the pic of Hook with Bae, he already has his hook, so, this is after Rumple killed Milah and took Killian's hand and he went to NL using the bean. Going by the 'six months later' caption in the promo, I'm going to guess that means six months after Bae went through the vortex, which happened years before Hook became Hook and went to NL. So, if that's the first time Hook visited NL (which I think it is) Bae was already there for some time, making me think that Hook can not be Pan – we see the shadowy figure before Hook would have made it to NL. Also, there's a book by Hugh Holton “Devil's Shadow”. In it, one of the main characters is named Ian Jellicoe (name printed on the cart in the promo) and he's from England. Not that the book itself has much to do with OUAT but the title – Devil's Shadow – and the shadowy figure (looked devilish) and the fact that Bae 'goes through the window' to get into the Darling's house – all kinda fits together. I think there is still a good chance that Bae was in fact Peter Pan.