While Mockingbird is the frequent love interest and ex-wife of Hawkeye in the comics, on Agents of SHIELD she and Hunter are an item. Or at least they are when not bickering about their romantic past. Both characters debuted this season along with an expanded cast, and have been a key part of the ongoing battle between Agent Coulson's SHIELD and another group run by former SHIELD higher-ups. At this point the series has yet to be confirmed, and we don't really know what it will be about. It could be another large ensemble, or maybe the focus will simply be on Morse and Hunter, which sounds like Moonlighting Marvel-style. The pilot is being written by exec-producers Jeffrey Bell and Paul Zbyszewski, with the latter eyed as the showrunner. As for plot details, they'll supposedly be obvious by the end of this season.
Add this to the mysterious series 12 Years A Slave writer John Ridley is developing and ABC might just be rebranded the Marvel Channel. I'm actually not kidding about that last one. Don't be shocked if there is a Marvel Channel at some point soon. Why the heck not?