Creating an environment means you have an idea how of the sky, lighting and colors of the scene look. By adding a tonemapper to the mix, which is hidden as an advanced graphics setting and defaulting to a different one than we have been using to build our PBR content in the past year feels counterproductive to the effort put into said content.
The tonemapper could instead function as a parameter of the EEP sky. Default all legacy settings that have not been resaved under PBR to Khronos, default ones that HAVE been saved under PBR to ACES-linear mix, and make them all editable to whichever mapper+mix level as desired after the fact. Additionally, add a feature to override the EEP tone mapper to use a fixed one instead of environment-based, giving the functionality that exists right now in viewer 7.1.11 - one tone mapper to rule them all.
Discussion on the subject and source for the idea: https://community.secondlife.com/forums/topic/517003-khronos-tone-mapper/