I see. In that case, I don’t think you would need one cell per minicolumn either (cells could just go away, leaving minicolumns and segments).
One potential issue I see is that this would function similarly to vanilla HTM configured to have max segments per cell set to one. There are some other conversations on the forum related to that configuration (for example here).
Of course, one big difference between this idea and the one-segment-per-cell idea, is that this strategy would also be equivalent to your idea of growing new cells on the fly. I’ve not seen that particular implementation before, so not sure about the benefits or drawbacks.