Although taxing PoBs works in theory we have no way of actually backing it up, with the reunified Kusari about to go into full swing it is very likely that our influence over things that are happening in the more central territories will become much harder to enforce. this is all speculation of course and we won't know until the next story update.
This could certainly be on the cards in the future depending on how the Kusari story plays out, would be great if we had an income besides pirating and smuggling so if you have some experience with this and how to implement I'd love to hear it.