Re: IM4 in Phase 3?
Part of me thinks that the new one-shot could hint at Phase 4 with a new Mandarin, the real one in charge of a company called Prometheus who may hire Ghost to break into Stark Industries to gain control of Tony's technology for himself so he can bury his rival. It would be a great way to establish a new lead actor playing Tony by using a familiar villain but not rebooting.
In Iron Man 5, Zeke Stane wants revenge as the second Iron Monger. He hacks into Stark Industries to release the blueprints for all of Iron Man's armors over the internet, hinting at a future Armor Wars storyline as well as steals all of his funds, leaving Tony as a homeless drunk. Demon in a Bottle is perhaps the most famous Iron Man storyline and crossing it with Five Nightmares only makes it that much sweeter. Iron Man 3 was about whether Tony was still Iron Man without the suit, Iron Man 5 would be about Tony losing his wealth and how in many ways he's defined by his riches. Here we have Tony at his lowest point where he's in many ways back where he was in a cave with a box of scraps.
Iron Man 6 is the full real Armor Wars storyline where Justin Hammer and his daughter Sasha have assembled a full team of armored enemies to fight Tony. It would just be a full out actionfest where the new trilogy is completed by going all out.
Granted, I'm not sure who will even be able to play Tony in Iron Man 4 come 2019 as it's a very long way off.