Alright, here’s my crackpot theory.
I think Jefferson is Rumpel’s son. The Blue Fairy said that she was going to send Bae to a world without magic, but a lot of people think she either lied or made a mistake and accidentaly sent him to either Oz, Neverland or Wonderland. Once the curse took effect, he was sucked out of Wonderland and placed in Storybrooke. Finding Baelfire is the curse’s main objective, so maybe the curse sucked Jefferson out of Wonderland and placed him Storybrooke. This may explain why he wasn’t able to leave the house for 28 years. Not because the Evil Queen was trying to punish him, but because the curse wanted to keep him in a safe and confined place so that it would be easy for Mr. Gold to find him. Besides, why would the Evil Queen choose to transport only one person from wonderland? Why him? Regina had a lot more important things on her mind to worry about other than some dude she left behind.
Jefferson’s magic hat may also be a clue too. The hat is able to transport someone to 16 different worlds. It’s a realm jumper. This is exactly what Rumpel needed to find his son. Maybe Jefferson created the hat so that he could find his father before the curse took effect.
There are also a lot of similarites between Rumpel and Jefferson. Rumpel became the Dark One so that he could save his son and give him a better life. Jefferson decided to work for Regina so that he could provide a better life for his daughter. However, in the process of trying to save their children, both ended up losing them in the end. And after they lost their children, they both went insane.
I also think Jefferson wants to rescue Belle so that he can reunite her with Mr. Gold, and accomplish what he was never able to back in Fairytale land. Break his father's curse. Jefferson is rumored to be sharing a scene with Belle in the season finale, so this may be his main goal.