Every currency is representative of what you can buy with it, as well as subject to fluctuation based on quantities the currency itself and of the items that it can be used to purchase. The best example I can think of relating to FFXIV would be warped arrows. Right now the current gil cap is just under 1 billion gil. 999,999,999 and the value of 1 gil is equal to one warped arrow. if this is an across the board 1/10th reduction of cost and cap then someone who has 1 billion gil will find themselves with 100 million after 2.0 (100,000,000) if this were truly a universal change in the value of gil then warped arrows would now be 10 arrows for 1 gil. (each arrow is now 1/10th of a gil in value.)

Someone at the one billion cap right now would be able to purchase the same exact amount of warped arrows as someone at the cap after 2.0 with 100 million gil. The only thing that would change is the denomination of the bill.

the problem with theoretical currencies like gil is that it's very hard to balance the amount of gil that exists at a given time.

inflation occurs incredibly easy in MMO's because of the notion of "Vendor Trash." I can spend x amount of time earning y amount of items and they will sell for z amount of money to an npc. That is money that is being created out of thin air. much like if the US decided that to pay off it's debt it was just going to print trillions of dollars. It wouldn't pay off anything because each dollar they print would make every dollar in existence worth that much less.

The best example would be percentage based. All of the gil currently in the game equals 100% of the wealth. let's pretend the game is brand new and not very popular... there are only 10 people playing and they each only have 10 gil. that means that the numerical value for 100% is 100. Each gil is worth 1% of the total wealth. Now let's say the game has expanded. there are 1000 players and they each have 1,000,000 gil. 100% of the wealth is now 1,000,000,000 gil. that means each gil is worth 0.000000001% of the total wealth. (I may be off a decimal place or two, if someone wants to correct me.)

In any system of currency, real life or theoretical values fluctuate and have to be based off of a specific item and are subject to inflation. A gil will never be just a gil.