Yep, the wanting to go back to WW2 was just before AW launch I think but the tweet about being excited to share what they're working on next came a few month later.
I doubt this was the case. Activision was going after Titanfall and all the hype that surrounded that game since June 2013. The game launched early 2014 (AW release late 2014) and it wasn't the mega success that everyone thought it was going to be aka the gamechanger of FPS shooters/COD4 of this generation.
I'm sure Activision reacted as soon as Advanced Warfare early sales failed to match Black Ops level and also knowing that Titanfall didn't had the lasting appeal that some people were predicting before launch.
Ehh Titanfall sold a lot (more than 7M), that's a pretty big success. Unless you mean content/longevity wise, but CoD is a different beast and is always jam packed with content so I doubt that was on Activision's mind. I mean Titanfall's longevity problems wasn't that the game wasn't good on a technical gameplay level, it was that there simply.. wasn't enough content. Gameplay wise everyone praised the hell out of Titanfall. I honestly think the change of heart was when people started to despise AW.
As for it being a gamechanger.. Honestly I'd say it did considering the past 3 CoD's have been futuristic lol and if CoD did the movement right, it probably would continue throughout this entire gen but they kinda fucked it up & it wasn't fun to play but that's a CoD problem. I know that's just CoD but what other MP shooters have came out since? BF1 is too late and Star Wars/Halo was already futuristic.
BO level is a high level to reach, AW sold more than Ghosts.
A lot of people were hyped for AW, pre release reaction was good, it had good worth of mouth for a few month post launch, futuristic shooters looked like the new hot.. I have a hard time believing Activision didn't go to them and say "Make AW2." because that's where it looked like the market was going. I mean, this is the company that has a 3 year dev cycle and all 3 are making the same type of game.