I think you are vastly overestimating the number of PDF sales to book sales.
People seem to think that PDFs sell better then DTF... and for some mediums that might be true. But for things like graphic novels, games books, and other "tactile" media, that's just not the case.
I thought for a long while that comics would just end up going digital, and that was where the sales were going. How wrong I was. Turns out that for graphic novels, PDF sales are only 8% of the DTF market. Comics are around 10%,,,, and I can only guess what games books would be at.
As to Piracy... for these niche markets, (games, comics, graphic novels) the estimate for piracy is actually very small. This is because the market itself is very small, and usually made up of dedicated people who support the industry, with piracy happening only on the "fringes" of the audience.
At least, that's what I am getting told..
Oh, I'm almost certainly overestimating things. Still, you only need one person to buy the PDF and scrub the watermarks in order for them to post it online somewhere.
I definitely think that the impact of piracy on RPGs is smaller than 75%, 50%, or even 25%. If you count illegal downloads as "lost sales," then maybe those numbers might add up, but that's flawed reasoning. If someone can't afford to buy an RPG, or wanted to "test drive" it first but didn't have a friend with a copy, then they shouldn't count as lost sales. In fact, the latter group might be potential increased sales.
Studies of video game piracy show that it either does nothing or
may even improve sales. There's a lot less info about board games, only a few articles about counterfeit board games sold in China and other countries where shipping costs make board games too expensive for the average user (Or where the local law just doesn't care about IP). And everything about TTRPG piracy that I was able to find was speculation, forum threads, or individual developers' opinions on the subject.
And there's nothing to support that an early PDF release would increase the rate. I'll believe that the original 6e PDF piracy impacted sales, but I also think that bad reviews would have done the same thing.
I don't think TTRPG piracy rates are well understood enough to make the assertion that piracy of 6e caused a 75% drop in sales. I think it would be fallacious to then apply that to piracy of any book, since 6e's release was "special."
Given their editing woes, do you think they could actually find someone to format, index, and link a PDF in a useful way? 
I remember the 5e core book...
6e actually does link to the correct pages. Can't fault it for that
Sometimes NDAs are frustrating because they make gossip impossible.
Anyway, to quote Discord:
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And here are the upcoming books according to Jason Hardy from a Facebook post.
Upcoming:
Slip Streams (plot book)
Collapsing Now (Threats-like book)
Street Wyrd (core magic book)
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Will see when exactly. Looking forward to customizable spells myself. Also <spoiler> and <spoiler> in Collapsing Now.
Tricky tricky. What if you did the spoilers all in klingon? Hardly anyone speaks klingon...
