I think it was a video on Matt Risinger's channel. They basically furred out a chamber below the roofs sheating with OSB or something similar for ventilation, sprayed the (closed cell?) foam to the desired R-value to the underside of the OSB and then installed the ceiling finish, capturing the foam as you propose with T&G. I would wonder if something cheaper than OSB could be used to create the chamber as it would not have structural value.