Well, phase one was Ironman/Thor/Cap/(Hulk) film series to make the Avengers film series...
phase two was tv. Agents of SHIELD/Peggy Carter.
phase three is a second round of films... the phase 1 sequels + Guardians & Antman
phase four is streaming: Daredevil netflix series will cross over with Jessica Jones, Luke Cage Ironfist (all confirmed) to equal Heroes 4 Hire.
Right now Marvel is considering the viability of Blade, Doctor Strange, Ghost Rider as a block (Midnight Sons)
Maybe webseries? IDK... but they already did a meeting with Wesley Snipes.
And at some point I imagine they would add Punisher to the netflx stuff the way they added Guardians/Antman to the movies.
Black Panther is coming.
I'd say the end goal is just
get Spiderman & X-Men back before Stan Lee passes.
If you just mean storilines... they have plenty of Avengers stories they can do after Civil War. The obvious choice being
Secret Invasion.
They already set up the alien angle with Guardians of the Galaxy and it would give them an excuse to cameo everyone.
Other events that would require the whole team is Atlantis Attacks story arc vs Namor. Even though Thanos is huge, there are lots of other villains powerful enough to require the Avengers to Assemble. Onslaught (if they get X-men back)... the Masters of Evil. Doom (if they get Fan-4 back). Taskmaster. They could also introduce Citizen V and the Thunderbolts since Baron Zemo is in the Captain America: Civil War movie.