Being real here, you could only add perks to pkp-store that make pking a bit more convenient. It wouldn't be a legit way of making money, not with emps and it's economy.
But to be honest who gives a fuck about teleports, armour fixing or vecna-whatevers that are suppose to benefit the pkers, what would really benefit the pkers would be not häving to wait 2 hours for a single fight.
Not that all of these perks and ideas regards to pking-shop are shit, just leave them for pvm/skills/minigames. Because players who have a pk-store and no pkers to kill will eventually give up on pking anyways.
Just try to grow the server is possible in other ways, and pking will grow too. wat im tired
Also when I last played there were decent amount of pkers around so Im not trying to press on the issue that pking is dying. But honestly pking doesn't need some gimmicky updates either, stick with balancing the general pvp not spend time on useless gimmicks.
edit: again, not that you can't come up with good ideas to pking/pvp shop. But I think that it's fine as is, and coding time should be focused more towards rest of the game.