Sure, they could show even more of Neal in flashbacks. Like, what he did after leaving Neverland. How did he forge a new identity? Did he always live in New York after fleeing Neverland? Or he could have possibly gone to another world before that?
Adam Horowitz saying, "Absolutely. We would love that" in response to a tvline question about whether they would like Neal to come back for a flashback is not a definite confirmation that he will be back for season four. In the past, the writers have expressed interest in doing lots of things on the show prior to season three, but many of those things we never saw in season three. I'm not saying the writers lie, but they never express interest in bringing something on the show *and* also state when we will see it/them/him/her unless they have already planned for it to happen. So it's possible the flashback with Neal *can* occur in season four, but it also may not depending on what the writers actually have planned.
The Son of The Dark One, the Master of Loopholes, The IMMORTAL, Most Powerful Sorcerer in the Enchanted Forest, dead ! Come off it. The scriptwriters realy are desparate to get a romance going between Emma and Killian. They realy are losing their emagination. Now if a (Go'uld) Sarcofhagus had been around in The Queen's crypt that would have been inconvenient. But as The Dark One is such a jackdaw, there must be at least one Ring of The Nazgul, or some equivalent Daedric artifact, in His shoppe. With that and some necromantic magic, Neal could be restored as a realm hopping Wraith, able to fully manifest in Storybrooke and magical realms, and as a ghost elsewhere.
To be fair, the writers have been dropping hints of Hook's feelings for Emma for a long time all throughout the third season. I wouldn't say Emma was reciprocating until the very last episode when she kissed him. I think it's tied up some loose ends. This is a lot better than continuing to see Neal and Hook fight over Emma cause I hate love triangles.