You're all presuming that the next "Avengers"-tagged film will be the Infinity Gauntlet story with Thanos as the big bad and basing the rest of your reasoning around that being taken as a given...
Think about it, We've got all these new characters coming into the MCU who are likely to pop up, albeit briefly, in a Thanos/Infinity Gauntlet movie, and we've also got the likes of the Inhumans who need introducing, plus there's the existing Avengers and GuardiansOfTheGalaxy.
There's no way that following
Ant-Man/Captain America 3/Doctor Strange/Thor 3/GuardiansOfTheGalaxy2 we're going to get just
one more movie (Nov 2017) and then go straight into the face-off with Thanos.
The newer characters would
either seem under-used
or unnecessary to the audience depending on how they'd been previously received, and I really don't think we're going to get
Inhumans in the same years as
Thor 3 and
GOTG2 and then the Thanos story the following year, That would all just be too cosmic-heavy, which is why I'm certain the Nov 2017 movie will be something earthbound, most likely Black Panther.
Now there was a rumour a while back that "New Avengers" would be the flagship movie of Phase 4...
...I think that may have been the original plan, but they've brought that movie forward to May 2018 to get that "New" Avengers team
(Doctor Strange, Quicksilver, Scarlet Witch, Vision, Ant-Man, Wasp and Black Panther?) established prior to the big face-off with Thanos so that they come across as a functioning "team" in the same way the other Avengers and GuardiansOfTheGalaxy are
(and by then also Netflix's "Defenders"?)...
...so I'm still leaning towards...
MAY 2018 - AVENGERS 3 - new team movie
MAY 2019 - the WHOLE of the MCU vs THANOS with a title that doesn't make it just about the Avengers
EDIT: In which case, I'd say for the other 3 slots we're looking at
Black Panther, Inhumans and one from
Captain Marvel/The Incredible Hulk 2 with the other appearing in Phase 4.