Even in FFXIV we have something like that

Most common solution for this is just like experience points:

The longer you log out, the higher the time you will get "FFXIV Gil". 

This is a proven system seen in many other games!

Even in Buy Cheap FF11 Gil we have something like that, its just sad the blue XP bar does have a max limit...

 

The keydesign of this system compared to the fatigue system we had in 1.0 and why players suggest and complain since 1.0:

While the fatigue system punish the Final Fantasy XIV players who are too fast the other system just doesnt. 

 

As example experience points:

It is designed to have a curved system, the higher you get, the longer you need for next level up.

If you normally play without any breaks you will have to spend the normal time to get maxed.

If you make breaks and logout there is a "bonus" added to your xp gain and the longer you are away, the higher that bonus becomes or the longer you can use that bonus. 

Technically its called linearization: The difference to the new curve becomes the bonus. (math)

 

Edit: Players tend to finish a class or content before beginning a new one, with brickwalls SE is forcing the ffxiv players to play other classes before content is finished and that makes organizational matters just more complicated. You will need more lists of what you have and what you need ... While with the fatigue system you could at least play the other class normally, with the tome cap we are blocked out for the week whether we play another class or not. If you play healer, tank and DPS, have fun waiting months to get the gear with tomes in http://www.mmo4pal.com/ffxi-gil/ ! (Some like to have it for vanity - mixed gear just looks ugly!)

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