While Age Of Ultron was always designed to a set-piece at the end of an arc - and a satisfying full-stop to the Phase - the MCU is a perpetually evolving thing, and there are several clues for how the events will impact future films. Beyond Easter Eggs and the mid-credits sequence that reminded everyone that Thanos was still a thing, the film teases new relationships, old frictions and a whole world of possibilities for the shape of things to come.
And by the look of it - as the emergence of a whole new Avengers team and the vague promise of some peace for a couple of the veterans teased - Phase 3 is going to look significantly different to the already completed arcs. There's not quite the dramatic fissures open that some fans might have expected going into Civil War, but then the Avengers movies are probably the only MCU films that actually necessitate a happy ending. That's sort of their job.
Obviously Phase 3 will bring a raft of new characters who will further complicate matters, but speculating how they will impact on the race to Infinity Wars and beyond is something of a minefield at this stage. However, even where those characters are concerned there are hints in Age Of Ultron at how their stand-alones might tie in with the pre-existing characters and storylines.
14. The Human Cost Of Superheroes
As was teased in the run up to Age Of Ultron's release, Marvel have seemingly taken a lead from Man Of Steel in investigating how the collateral damage caused by superheroes saving the world impacts in human cost terms.
That is clearly the specific angle they're following for establishing the plot of Civil War; a similar approach to the comics arc, of course, though they will presumably (or hopefully) avoid the superhero reality TV show that proves to be the touch-paper on the page.
With Ultron having probably killed a significant number of people even without his plan going off properly without a hitch and the enduring image of Hulk rampaging burned into collective consciousness, it's not going to take a great deal to gather support for Superhero Registration.