That was quick… the very next day after we reported that the Ratatouille ride in Paris was still showing the various scenes in 2D, we have now heard from two guests that everything was switched back to regular 3D once again.

(5/21/19) According to a reader who visited Walt Disney Studios Paris this week and loved the 2D version of the Ratatouille dark ride. They did ask about why the ride was playing in 2D now instead of 3D and were given the excuse that it was just undergoing maintenance and would eventually return to using 3D projections. Of course this could have just been the line the CMs were told to give guests, or it could be that Disney is just conducting a guest satisfaction study to see if guests enjoy the ride more without 3D glasses than with, as they are preparing to launch the new version at Epcot in Walt Disney World.
Time will tell if the Paris version says 2D or returns to being in 3D.