I'm not really a fan of the VIP systems in games in general. There is no way to make a VIP system that feels worth it enough to get but not so worth it that you don't feel like you're missing out by not having it. Either it sucks and no one wants it, or it's good and everyone will want it but some won't have it and will have a worse gaming experience because of it.

Selling inventory slots and character slots is a perfect example of creating a problem and selling the solution. The devs are actively capping your inventory in the hopes you will feel like you don't have enough space and will be enticed to buy VIP. And this is how this kind of system starts. If not enough people buy VIP they will have to start doing other things to entice you to buy it. XP boosts, currency boosts, log in rewards, and so on are examples of what they will eventually have to add if VIP isn't successful enough. There is no finding the right balance here. There is no right balance. You either don't need VIP and the system will be basically unused or you will feel like you need it for "convenience" and then it's just a matter of if you can afford it or not.

I honestly like the idea of the new skill but hiding it behind a paywall is pure and simple pay to win. There is literally no reason not to use this skill when not playing. Except maybe if you want to do a specific hang out I guess. So essentially what you've actually added is an xp boost system dressed up and disguised as something else. Sure it's a bit difficult to use as you have to level it up, but that's what it is, an xp boost.

So what would my solution be? Make the game free to play up to level 10 or 20. Kinda like how the demo is now. Then add a monthly subscription that everyone must have to play the game beyond that point. I know this probably won't be popular with everyone and especially newer MMO players but this system allows players to always be on equal footing. It's basically the only way to do a monthly sub where there aren't pay to win elements added on.

The other option I guess would be to make VIP purely cosmetic. Fancy VIP dyes, VIP character models, VIP armor/weapon skins, etc. I personally am not a big fan of this system because it always ends up with VIP having the best looking items and you don't earn them, you just buy them with your money. So maybe, make it a VIP crafting skill with items that only you can use, or make it so VIPs can do certain quests that non-VIPs can't that allow you to unlock these cosmetics and make the quest chain long and difficult. That way you aren't just handed the best looking gear but you still need VIP to get it. And I'm talking purely looks. This should be some sort of transfmog if you go this route.