i know, many people will think there is zero chance that this could happen, ffxv were released 6 months ago. But i think that the work for the next entry could started already 2 years ago, i don't believe they waited for finishing part xv. SE is a big company with many developer teams, and this time could going all a little faster, wouldn't take the long time for ff xv for comparison (first it was for ps3 as versus, than they started all over again for the new generation as part xv). From last interviews like:

On Final Fantasy XVI

With Final Fantasy XV, Square Enix was able to fuse a setting that is both a modern and fantasy world in one. When it comes to main-numbered Final Fantasy games, the directors think of everything from scratch with each installment. That said, it doesn’t mean we’ll necessarily see a modern setting for Final Fantasy XVI. Hashimoto says that they haven’t made anything for Final Fantasy XVI yet, but to keep in mind that just because Final Fantasy XV has a certain setting, it doesn’t mean the next one will follow in the same way.

Hashimoto emphasizes the differences we’ve seen in main-numbered Final Fantasy titles by using VII, VIII, IX as examples on how we saw it go from a very steam punk cyber world in Final Fantasy VII and then back to more of a fantasy world in Final Fantasy IX. He says that this is something that directors might do on purpose to change things up for the series.

As far as the battle system goes, this is also something that is decided by the director, so it doesn’t necessarily mean Final Fantasy XVI will be more on the action RPG side as we’ve seen in Final Fantasy XV. Hashimoto says when they start work on a new Final Fantasy, they set the bar to make the ultimate fantasy of the generation with each installment. So if a director feels that a certain battle system would work best in the current generation, that’s the main system they’ll go with.

Read more at http://www.siliconera.com/2016/11/09/final-fantasy-brand-manager-talks-possibilities-final-fantasy-xvi-x-3/#BEmjCAq7T63stBmk.99

We know that the next entry could go in the direction like ff ix has gone. Maybe i'm too optimistic, but one thing is for sure, it would be one of the big e3 moments, if SE would all surprise us with a first trailer of the next entry of the mainline series.

I think it might be too soon, but I don't see why a teaser is impossible, either. It would depend on how much effort has gone into FFXVI ever since FFXV was in the last stages of development.

Yes, release date holiday 2016

I don't think we will just because: 1. Not all the story DLC for 15 is out yet, 2. Dragon Quest and Kingdom Hearts are probably going to be in the forefront this E3... maybe. Well I think the chances of seeing KH info vs new FF are higher. I think next year or maybe before the end of this year we might get a teaser for FF though

No, they'll show Final Fantasy Versus XV, then in 10 years they'll release Final Fantasy XVI instead.

I get the feeling we won't hear about Final Fantasy XVI until next generation.

They've already got massive teams on FF7 and KH3. Doubt there'll be another huge game until 1 of those is out.

They already showed Final Fantasy 16 - Agni's Prophecy

It's long overdue already. Should've come out last E3.

Hope so.

I want to get FFXV out of my memory asap.