Sure, the audience needs to have a sense of continuity. And serving a bit of the Hulk once in a while – even in post-credit scenes or in a flashback or whatever – is a way to reassure the public the Hulk is still out there in the MCU.
But, then again, why should we assume he won't be a major player in the events expected in Civil War? Just because he's not confirmed – yet – are we supposed to conclude he won't be included?
As much as I'd like to see Mark Ruffalo reprising his role in Captain America: Civil War – full-blown role, not a mere cameo – I have to admit there is a possibility he won't play a major part here. But granted, he'd definitely and considerably tip the scale in favor of however he sides with, if at all!
Anyway, I don't rule Bruce Banner out just based on the fact Ruffalo is not announced!
Scott Derrickson's venture programmed for 2016 will introduce this established comics character on screen. It might or it might not be an origin story, but that's not the point here.