I don’t think this shmi-theory will be in IX. It doesn’t bring Anakin’s arc full circle. Only by wandering down the reylo road Anakin(Ben)'s story can be complete. There have already been enough evidence for this (similar concept arts, themes, shots) to say that the theory is pretty much a safe bet.
I’m more interested in how they will reveal that Ben is Anakin and Rey is Padme (if this is indeed the case) and how the fandom will react.