Do we even know what portion of the initial game purchase and monthly subscriptions go toward development? Obviously it isn't 100%. The devs don't get to keep all the money to pay themselves with, then decide where to allocate the rest of the funds. The money goes to Square Enix, who makes all kinds of products. It is reasonable that the company will attribute a higher budget to a game that is performing better than others, but it's not like it's a 1:1 ratio of "you make x amount of money, you get that money put back into the game." SE rakes in the revenue FFXIV gets, uses it to pay for business expenses, funding other projects, employee salaries, etc. And whatever is left over, they divide up where they see fit and decide on a budget for each game. And even at that point, the budget is not purely a "Make the Game Awesome Fund" -- a huge portion goes into marketing, merchandise, hiring staff, server maintenance, and other stuff.

I don't think we will ever get any stats about how much of the game's profit goes back into actual "game development," because not only is that a vague term, but the percentage probably fluctuates constantly based on the company's whims.

All I know is, Square Enix took in our subscription money and decided to use it to create the cash shop. I'm not confident that the cash shop profits will be used any differently.