In the comics, SHIELD has LMDs (Life Model Decoys) which are robots that look like certain specific people and are programmed to behave like those specific people. They would be used to stand in for important people in situations that could be dangerous.
I currently have two theories:
1) Agent Coulson did die in The Avengers and Agent Coulson in SHIELD is a LMD of Agent Coulson. This leaves the door open for Agent Coulson LMD to evolve into The Vision later on down the road.
2) Ultron is the baddie in Avengers 2. In the comic books, Ultron is created by Hank Pym (one of the founding Avengers aka Ant Man). Ultron could end up being a SHIELD LMD that malfunctions (gains artificial intelligence) and decides to destroy SHIELD.
1a and 2a In the comic books, The Vision is created by Ultron as a slave/weapon against The Avengers. Ultron could interact with the Coulson LMD and strip the LMD of its Coulson personality starting it down the road to becoming The Vision.
Joss Whedon is running The Avengers. His brother Jed Whedon is running the SHIELD tv series.
It could be just as easy as Ultron comes across Coulson LMD in Avengers 2, Ultron mentions Coulson is a robot, shuts Coulson down/erases him, and then the storyline continues in SHIELD tv series (of what happened to Coulson after he died in The Avengers, and his progression/transformation into The Vision)