Personally, I think 1 and 4 are the most viable. For (2) It'd be hard to restrict usage of a ship outside of ID requirements. (3) would really only benefit the big PoBs, not the smaller ones maintained by one person, because it'd become that much harder to maintain the higher core bases just to stay afloat.
I can't speak to the dev process of implementing the changes, but knowing I could store more for the amount of work I'd be putting in would make me more likely to invest in a PoB just for my own purposes, rather than just banking for a barge and having no maintenance concerns.
*Edit* - or if there was a way to implement a bulk surcharge somehow for purchases over 5k, that could benefit the PoB owners who are getting drained quickly.
