I was wondering that too. Im surprised they didnt put this in beta first for players to hit it.
With the overall scale of the changes, I'm not sure how much good a public beta would do. To get any proper feedback, you need to do entire play-throughs to test the various encounters and mechanics. That's the sort of task in-house QA can do pretty efficiently.
Turn-based isn't something that is toggled on or off. It is a permanent choice made at the beginning of the game. While players might be able to comment on UI or basic things, it seems unlikely that many beta testers will push through the game over the course of a weekend to see how turn-based affects the balance of late-game encounters.
Edit: Later articles make it clear that *everyone* is getting this as a testable addition to the game. It isn't just going to a self-selected pool of beta participants.
Edited by Ethics Gradient, 22 January 2019 - 07:52 AM.