This game uses lots of Square Enix' mobile-free-to-play-game practice such as FFBE or FFRK. The difference is in the free to play games you keep, in this game you only rent. But both are designed to siphon as much money as possible.
inventory space space is designed to be used up fast, the devs say it's hard to increase your space due to memory issues, but you can pay 2 dollars extra per month to rent more. Up to 6 times.
Weekly cap is basically the energy system, every 10080 minutes your energy replenishes. Instead of regenerate for free, it's taken out of your sub.
The end game is items, a simple line of code. They are gated behind RNG or gil, more likely RNG. RNG gates lots of the core game components such as gears, crafting, weapon upgrades, materia melding, etc. Participating raids and extremes are none RNG on paper, but RNG in practice. Because they require people, and people are unpredictable. Once you complete main story, the game will mainly use the dailies and RNG formula to keep you playing, there will be new contents, new bosses, and new events. But the main game is still RNG, just like SE's other mobile free to play FF games.
Now that's established, I did remember reading somewhere the inventory space is due to increase. I wouldn't be surprised even if they introduce additional inventory space, it'll be behind a real cash paywall. It's going to be something cute like Fat Chocobo's S/M/L/XL/XXL Item Sack. The sack is free, but to summon the fat bird you need to buy a one time purchase of (insert name) greens with IRL money, different green for different size of course.
I'm looking at all these hints, veteran rewards frequency, mog station exclusive, eternal bonding packages, jump potion. The devs are nudging, test the water out, see what they can get away with, and they are patient. They won't do anything obvious, but they are conditioning people. After all water can pierce rocks given enough time and persistence.