I actually don't need to, never claimed I did. All I've done is shown that it's not exact science like people here try and claim it is. If someone is going to try and use this stuff as an exact answer then they need to include every angle and every possibility which doesn't happen.
As someone who works with the numbers of a big company, I can tell you that there is a lot of predictions that go on. There is no exact data that will give you the correct conclusions. You look at what you have and work from there.
Basically what Wizards is most likely going by is their PHB sales numbers. They figure everyone who plays probably has a PHB. I can tell you for a fact that is false.
Of course there are a lot of predictions going on. And when they released 5e they predicted that a change in their publication model would boost sales of each product. And from what I've heard, it has. If the prediction works, you stick with it (and build on it).
Just because there may be other products that
might sell well, they do have hard sales numbers that seem to indicate that the 5e plus their new publishing approach is working very, very well.
Anecdotally, current Amazon sales ranks (books in general, not RPGs):
HotDQ 5414 (Aug 2014)
RoT 7143 (Nov 2014)
PotA 6384 (Apr 2015)
OotA 6386 (Sep 2015)
SCAG 3212 (Nov 2015)
CoS 3395 (Mar 2016)
SKT 2815 (Sep 2016)
Without historical data, we can only look at what it showing now. But SCAG is selling around the same numbers of the last two APs despite being a year old. That's a good sign.
HotDQ is outselling all of the other APs that are over a year old, which is interesting as well (Particularly since folks don't seem to feel the sequel is a necessary finish). I think that supports my belief that the APs are best suited for non-campaign style groups, that pick up the book, make a group of characters, and play for several months. Fewer continued with the same characters to the direct sequel. The sequel on its own (like most sequels) probably isn't selling as a standalone. It's most likely only selling to those that choose to play the whole AP through both books.
As a business, they have taken surveys, and they have put together a business plan based on these surveys, and they have put that plan into action. The fact that sales seem to be up across the board is a pretty good indication that they
are publishing what the players want. The fact that they continue to release two APs each year is probably a good sign that they continue to sell well.
They have been fairly conservative in their business model this time around. Late last year they added to the AP mix with SCAG. This year they did VGtM. So it seems that the current approach is 2 APs and 1 non-AP book. Perhaps they'll bump that up to 2 non-AP books. But it shows that not only is their business plan working, but they are building on it, and, it would appear, giving people what they want.
In any event, I think that the sales show that the business model is working, and the fact that SCAG is still selling well comparatively is a good sign that it did well too. So I wouldn't be surprised to see another book in a similar vein in the future.
It also wouldn't surprise me if we saw another campaign setting before we see another FR book. Expanding upon Ravenloft would make sense, since CoS seems to have done well.
I doubt they'll do a big FR Campaign Setting, since they'd pretty much duplicate what was released in SCAG and the APs for the Sword Coast. The Adventurer's League adventures are all set around the Moonsea, it would seem that a Moonsea/Heartlands approach would make sense for the next region.
