I know this may see like craziness but think about it. I really like characters like the Punisher, Daredevil and Elektra but i don't think they have quite the same popularity like Loki does right now. Loki has a huge following because of the Thor Movie and The Avengers so making a Loki TV Show starring Tom Hiddleson would rake in all the money for Marvel and would be the safest property to go with.
What makes me think this is actually possible is the fact that Loki is getting his own Marvel Now Series ( Which personally i am looking foward to). Maybe Marvel are testing the waters for a Loki TV Show..who knows at this point..
As for the story i would manly set it on Earth with flashbacks to Asgard. I would set it after Thor: The Dark World. Loki apparently died in T:DW but is actually alive and is on Earth hiding himself until the time is right for him to come back and strike until he is captured by Abigail Brand and SWORD who tells Loki that he is forced to help them as a Agent of SWORD. Initially he refuses but Abigail tells him that he has a device in his right eye and if he does not join or betrays SWORD. Abigail will flip the switch which will kill Loki. Having no choice but to accept Abigail's offer he now works in the Shadows as a Agent of Sword. Combating supernatural forces and committing acts requested by SWORD while keeping his identity a secret to everyone. He meets plenty of supernatural characters like Ghost Rider and Blade and teams up with fellow SWORD Agent Carol Danvers on occasion.
These are just some ideas i have for a TV Show starring Loki