My two cents here - note that this is just my opinion and hope for the future
I am all for the 3rd exp for GD. GD2 is a sure thing but wont be reality until years from now and it would be nice for GD to get that little extra bit. GD2 aside, I don’t want to stop playing GD for many years to come and small bits of content is always welcome
Now Zantai said it is a financial decision and game, forums, reddit, steam etc feel like they are teeming with new players with more coming every day so I am hopeful in that regard.
As for the bloated content argument and balancing problems - Crate proved again and again that they are more than capable of handling issues as they arise and could deliver content which hits that sweet spot. So it is their judgement that I wholeheartedly trust in regards to what and where would be added to game so it doesn’t feel like too much or too little.
That said, if they make a third expansion, it should be on the smaller side with quests unrelated to Aetherials or Chtonians and also final expansion imho.
My personal wish is that GD gets one more mastery (thats a big wish, I know) and for some arctic and icy levels which are sorely missing up until this point.
As for some kind of announcement - I doubt it will happen before XBOX release - it makes sense both financially and from a timeline perspective.
That said, Crate will do what they feel is right and if we do get one more exp (which I hope we will) - they have my money for sure 
Sorry for the wall of text