Parmandur
Book-Friend, he/him
They already tried that unsuccessfully, the time needed to churn out a novel simply doesn't line up with the release schedule of the APs. That's why all the novels with the RoD tie in didn't come out until we were already well into CoS
They simply underestimated the difficulty to sync those two media
Which was of course double disappointing, meaning all their pep talk during the lead up to 5e and the sundering where they promised to get an internal "realms traffic cop" to make the continutiy even more tight and avoid lore errors, etc. was just outright lying to the realms fans to just keep them quite.
I also still doubt that as the reason. They haven't even finished the script or the casting yet. The movie is easily 3 years or more away. Way too early let everything drie up in expectation of a movie that might not even be in theaters yet in 2020. They could finish entire new novel trilogies by the time the movie is close enough to finish to start with earliest advertising
As I understand it the script is done, and Warner Bros. (the premiere makers of fantasy film, critically and commercially) start filming in a few months.
That means a 2018 release, probably, and a novelization of the script is inevitable. Everything screams "this is about the major D&D motion picture," whether that works out or not. And as to working out, the new stuff is coming from tip filmmakers, not...whatever that old thing was.
Doubt they lied, bit maybe after review they saw a fuzzy, non-metaplot heavy world as more conducive to fans. No more Times of Trouble or Spellplagues.