Apparently October 15 has been suggested as a release date for Pixel devices to get Android 15 (even though it has already been released to AOSP) so I would say NOS3.0 would be released sometime after that, starting with open betas before going to a stable release, meaning it will take several months for all models to receive a version of NOS3.0.
My guess is they will probably start with the 2(a) and 2(a) Plus, (and possibly the CMF Phone (1)) then NP(2) and then NP(1).