Because conjecture is fun, I'm gonna hop in!
Just the next three movies for now, though I might do more later.
Iron Man 3: Mandarin, but with a tech-heavy origin rather than mystic. The Extremis program and Mandarin's rings will be closely related somehow, and Mandarin himself will effectively replace Mallen in an adaptation of the Extremis storyline. This will be a much more personal story than any MCU movie to date; Extremis will have close ties to Howard Stark and will force Tony to confront his relationship with his father. Tony's alcoholism will begin to rear its ugly head, he will alienate Pepper and Rhodes, but it will not be fully resolved here.
Post-Credits Tease: Nick Fury, concerned with Tony's increasingly erratic behavior, will invite Rhodes to join S.H.I.E.L.D. War Machine will start wearing a new suit designed by S.H.I.E.L.D. to take Iron Man out if it ever becomes necessary.
Captain America 2: Winter Soldier. The movie will switch back and forth between past and present...in the past, we'll fill in more blanks of the time Cap and Bucky spent together. These scenes will focus on a mission to recover alien technology the Soviets stole from a HYDRA base before Cap's team was able to hit it. During the mission, Bucky is exposed to the tech, which introduces nanites to his bloodstream, unbeknownst to the team...the Soviets notice, though. These nanites give him remarkable regenerative powers and slow the aging process to a crawl.
After he falls from the train, Bucky is recovered by the Soviets, brainwashed, and eventually becomes one of their most effective Cold War-era spies. S.H.I.E.L.D. is aware of all of this, but doesn't tell Cap until he is assigned to hunt the Winter Soldier down, shaking Cap's faith in Nick Fury and S.H.I.E.L.D. even further. The modern era scenes will heavily feature Hawkeye, Black Widow, and Hank Pym, who is introduced as an expert in nanotechnology...they'll all be helping him track down and stop the Winter Soldier, but Cap will eventually turn away from them. In the climax, Cap will bring Bucky out of the Winter Soldier persona, and he'll end up needing to defend him from S.H.I.E.L.D. and help him escape.
Post-Credits Tease: We learn that the Red Skull exposed himself to the same regenerative/anti-aging nanites before he was "destroyed" by the Tesseract.
Thor 2: Enchantress will be the main villainess, and she'll be working with the Chitauri. The entire movie will take place in Asgard and other dimensions; there will be hardly any Earth scenes, and they will focus on Jane Foster's attempts to reconnect Earth and Asgard. Thor himself will not set foot on Earth. When Jane arrives in Asgard, she will find the realm in chaos, without and within. There is heated debate over the fate of Loki, and if Odin is fit to rule, having kept the secret of Loki's parentage for so long. Odin grows weaker every time he has to send someone off-world, as he did with Thor. The Enchantress will be working behind the scenes, attempting to turn major powers against Odin, including Thor himself. She is working with the Chitauri to make Asgard more vulnerable.
Jane's arrival throws off her plan, and she will refocus her efforts on killing/removing Jane, while Jane works to reestablish the bifrost, or something similar, based on her research. Meanwhile, Asgard is under siege by the Chitauri, who are attempting to recover the Infinity Gauntlet. The Asgardians expect reinforcements from other realms if they can reach them, making Jane's work critical. The Enchantress, however, manages to banish Jane to a hostile realm. Thor will be forced to turn to a repentant Loki for aid in reaching her, as Odin is so weak that another use of dark energy might kill him or worse.
The pair manage to save Jane together, but it costs Loki his life. Thor returns with Jane to find Asgard overrun with Chitauri, and for the first time we get a clearer look at Thanos. With Jane's help, Thor and Odin are able to use the bifrost once again to scatter the infinity gems across the cosmos - Thanos' siege is successful, Asgard is in ruins, but he is only able to recover an empty gauntlet. Surviving Asgardians flee the ruins of their realm, overrun with Chitauri. Many flee to Earth with Jane and Thor, intent on forming New Asgard.
Post-Credits Tease: Thanos and/or the Enchantress picking through the ruins of the Vault. They come across the Orb of Agamotto, granting them the ability to find the gems. As Thanos closes his fist around the Orb, we flash to the Sanctum Sanctorum. Dr. Strange, meditating with the matching Eye of Agamotto, wakes from his trance.