For posterities sake:
having done more research, this is what I know so far. As far as I understand, cell elongation seems to be an indicator of a bread reaching it’s full expansion capacity. Cell elongation is distortion of the bubbles within the gluten matrix, the fact the distortion exists as opposed to it simply collapsing shows that the bread can withstand the said deformation and expand fully. Good papers to start off with are:
Galliard, T., 1990. The microstructure and gas retention of bread dough. Journal of Cereal Science 12, 15–24
Rogers, D.E., Day, D.D., Olewnik, M.C., 1995. Development of an objective crumb-grain measurement. Cereal Foods World 40, 498–501.
Gandikota, S., & MacRitchie, F. (2005). Expansion capacity of doughs: methodology and applications. Journal of Cereal Science, 42(2), 157–163.