As we learned in the last few minutes of Marvel's Agents of SHIELD on Tuesday, Brett Dalton has returned as Grant Ward and will be part of the final story pod, likely to be called Agents of HYDRA. How this works is that there is an alternate reality inside the Framework, allowing for a character like Ward to not only come back, but to be on the side of the angels as we believed he was in season one. But if Marvel is setting up this alternate reality, maybe they'll go even further and bring back some of the other fallen agents.
Some fan favorites that could make at least a brief come back would be: Antoine Triplett (B.J. Britt), Lincoln Campbell (Luke Mitchell), Bobbi Morse (Adrianne Palicki), Lance Hunter (Nick Blood), Mike Peterson (J. August Richards), Andrew Garner (Blair Underwood), Robert Gonzalez (Edward James Olmos), Victoria Hand (Saffron Burrows), Felix Blake (Titus Welliver), Jasper Sitwell (Maximiliano Hernandez) and Isabelle 'Izzy' Hartley (Lucy Lawless).
Sadly that list can't include John Garrett (Bill Paxton).
But the writer's of the series basically just gave themselves carte blanc to bring back any character / actor from anywhere in the show four year run so far and use them in completely new ways. Which means that the unseen woman Leo Fitz (Iain De Caestecker) is helping out of the limo could be a lot of different people from Aida (Mallory Jansen) to Mockingbird.
And whose to say, other than the budgeting office, that Nick Fury (Samuel L. Jackson) or Maria Hill (Cobie Smulders) can't make an appearance again.
I'm very much looking forward to when Agents of SHIELD returns in April.