The FFXIV community has known for the past... one and a half to two years that Yoshida was producing something (but not directing it) that the rest of Creative Devision III was working on. What that was... no one knew. Now we know it's FFXVI. I can absolutely believe they've been working on it the game for four years if you include all the concept work that would go into making what is essentially a brand new IP in terms of world-building, characters, story, etc.
To give people some idea as to how "soon" things come out after Yoshids's division announces them... For Shadowbringers, the first fanfest was in mid November and dropped the first half of the CGI trailer, the name of the expansion and the general basic info about it including what two of the zones looked like in-game. The second fanfest was in early Febuary and dropped a slightly extended CGI trailer, more job info, more zone info and a lot of plot info. The third fanfest was in later March and revealed the entire CGI trailer, all the jobs, all the races and even more story details. The actual expansion released in late June.
So that's... seven months from when we first found out about the expansion to when it released. And yeah, that's for a game that is already out. But before that first fan-fest, there's honestly nothing indicating that an expansion is coming, let alone what it's called. The players kinda just assume it's coming because that is what has happened for the last six years and because Yoshida has mentioned that there will be a 6.0 patch series (and what plot it'll be wrapping up).
Given how far along the trailer for FFXVI is (all graphics are cutscenes or combat from the game, the VAs are from the game, etc.), FFXVI is really close to being done. While it's going to be more than seven months until it launches, it's not that hard to see the game being out a little over a year from now. Certainly two years from now it'll be out.
We even know when the next info on FFXVI is coming out: early 2021. So it's not even the situation where we have a game coming out eventually, but we have no idea when our next info dump will be. I wouldn't be surprised if the FFXVI dev team has a schedule of when all the info dumps for FFXVI will be until the launch of the game at this point. The FFXIV community had the timing on FFXIV info dumps (and patches!) all plotted out (until Covid hit) because that team kept to their release schedule like glue. And the amount of overlap between the FFXIV and FFXVI teams is staggering, so I wouldn't be surprised they're doing something similar.
