@FirstCavApache64 A square pyramid would better anyway.
@crimsonecho in fact if you had actually put some thought into it you would realise that it would be made to hold the same volume as it's equivalent fabric pot it's just that the soil that it missing from the top where it is not needed is in fact redistributed to the bottom where it can be made better use of.
Once someone does it, everyone will want to make it if it isn't patented. A zipper could be put in too in order to make it reusable for those who reuse their bags.