I agree that Hook needs to tell Emma. They are all in danger anyway and it looks like they will have to rely on Emma’s magic to ultimately save them since the writers have suggested Regina is not strong enough. Personally I was more disappointed that he didn’t just tell Emma upfront about the curse/threats than with the whole JR/Ariel thing.
I hate to theorize since I suck at it but I think Hook is going to end up telling Emma (or the Charmings) much like the Neal situation in Neverland and then they will go from there as a group pretty early on in the next episode. We are down to 5 left so I don’t see them drawing this out.