G.Leave
Cultivators Club
The idea of transplanting by sitting your pot on top of the finishing pot sounds like it could be a good idea. The roots in the top of the pot are a little different than the roots in the bottom though and your only allowing the lower roots to expand. I believe the upper roots are more responsible for oxygen intake then the lower roots. With the fabric pots this might not be a problem but I could see it not being as good with a plastic pot compared to just one large pot.
I won't worry about oxygen as the surrounding soil is loose and well aerated. My plan is different than stacking, I am planning to simply bury the pot up to the rim, and let previously air pruned roots to regrow into surrounding soil. With the directed slots in the herculese pots I think it should work out well.