It's doable. I won't ask people to do it, but you can make it to where people could actually be able to purchase basic cores and abilities and enforce the limits you need to.
- You'd need to code limitations for what you're capable of buying per the character's grade
- You'd have to define what is and isn't a core in the code.
- You'd have to define how many cores can be bought up to a certain tier.
- You'd have to make it public. What I mean by that is..
- When someone purchases a perk or a jutsu, it needs to notify people around them and the admin team themselves. Don't have it name specifically what the perk or jutsu is, just have it say they have purchased either a perk or a jutsu in a nondescript way. It's easy to tell if someone is breaking rules by going off that alone.
- I'd recommend giving admins the ability to toggle someone's ability to purchase perks and jutsu on and off. Essentially this would be a way to punish people that abuse the system or make an attempt to.
So it's definitely doable but it might come with a whole host of problems considering it's something else to check and code and implement checks and balances for. It's entirely up to the administrative team if they want to go about doing the work for it though.