Not sure, the parks have just relied on AP previews to fill that gap.
Since the "invention" of VQ, it's easily explainable why we haven't seen more traditional soft openings for new attractions.
- Rise of the Resistance & Hagrid - plagued with tech issues, got it ready just enough to get it working for opening day
- VelociCoaster - AP Previews
- GOTG, Tron & Rat - both ready way ahead of their opening dates, more than enough time to test, had AP previews
Tiana's ride system and operations will be identical to Splash... so not much testing to do with the public outside of AP previews.