Ok I get it and I’m with you for it being fully accessible firstThe work for the Type 10s will be, for the most part, very simple. Sandblast the platform surface, pour 6" more of concrete to the final 14" height, adjust ramps and stairs as necessary. Elevators are pretty easy - you just move the door frame and doors, and program it to stop at the new location. Some stations with stairs very near the platform edge might need slightly more aggressive modifications to prevent weird half-steps, but even that is not unreasonable. It's orders of magnitude less work than a full subway station renovation, and even rather simpler than a full accessibility renovation of a surface station, because the only thing changing is the platform height. All of the GLX stations, and likely other recent renovations, have been explicitly designed to permit the platform raising to be as easy as possible.
Full platform modifications for Type 10s cannot be done until it is certain that a Type 7 and Type 8 will never stop at that station again - the folding doors on those vehicles will stick on any platform higher than 8". That can be done branch-by-branch on the surface as soon as all service on that branch is Type 9s and Type 10s, which means late 2020s at the earliest, and cannot be done in the Central Subway until all 7s and 8s are gone. For better or for worse, all renovations till then will be to the lower 8" height. I certainly find myself in the camp of "make everything accessible as soon as possible, even if some work is duplicated, rather than waiting on an uncertain timetable."