MarkB
Legend
The "huge hit" part likely took them by surprise, so the earliest they could have been expected to react and start dedicating significant resources to it would have been around October to November last year - in a year where they already have most of their development efforts dedicated to this year's major new releases. It seems unlikely that they could have a product adapted, playtested and written up any earlier than around now.I think I'd prefer focused supplements rather than the apparent threat of microtransactions as a way to bring in more revenue.
I remember the bad old days of 2E and 3E bloat myself, but "hey, this game is a huge hit and it was created in such a way to get us a large part of the way through our development process for a book based on it" is a pretty conservative bit of additional content. They could even make it digital-only and not have to worry about printing or distribution issues.
And even then, there was no guaranteeing the game's ongoing popularity. Plenty of games are flash-in-the-pan affairs, great while you're playing them but soon over and offering little replayability, their short-term popularity soon eclipsed by the next AAA release. Even if they dedicated significant resources to rushing a product through, there'd be no guarantee that there would still be an audience for it by the time it hit the marketplace.