Personally I am for this system, up to a point. While it is not in common acceptance there is a point behind it. When you farm, fish, mine, whatever your intended system of gaining cash or gold in the game there should be a limit to how much you can do to help simulate realism. IMO FFXI implemented the change in fishing pretty effectively. Sure, it did not have the desired outcome of holding off scammers, but a real person would not be able to fish for 18 hours straight.
I do not agree with building a game where the system must be activated in order to advance to the high end content (in a reasonable time). I played FFXI and WoW for years. The difference in the game plays are noticeable. Back when FFXI first started in the NA servers, if you were not a caster (mainly healer) or tank, you could wait for hours for a good group. Also in towns you could sit down or follow a NPC and sell your characters items even while you were off the computer for the night. Should this passive time played be used against your account allowed time?
In WoW it was the same way for several years (new changes with cross-server dungeon groups) but all the classes could successfully solo up to a point even if it was slower rates of XP gain vs grouping. If you logged a character out in a town or Inn you gained "Rested" xp, which helps you level faster with gains from monster kills. While rested XP is not mandatory, it is helpful to a point. Since half of the leveling was from quests (in general, sometimes more or less) the Rested XP did not give bonuses for the quests being turned in.
As for a game being designed so you need the double xp gain, seems ridiculous. They are set up in a way to allow you to progress as the Devs. had originally intended, a bump in XP is just used to allow you to level faster to catch up, not intending for you to go into overdrive constantly (otherwise they would have set the XP rate that high in normal play.) While many people want to gain max level as fast as possible, when you put a game into overdrive it takes out a part of the game. In another argument it was related that power/speed leveling through your class without learning to play it, is the same as a ten year old going to sleep, waking up the next day and being 19, grabbing the car keys and crashing the Mustang through the garage door.
A true Fatigue system would be if you gain normal XP, then after your character gets tired you slow down. Casting gets slower, sword swings slower, etc. This would represent even the most battle hardened soldiers getting worn out. It will affect XP gain (not as a number or percent) but in the amount of time it takes to acquire it. While not a RPG take Left 4 Dead as an example. You could duck in a corner under a stairwell and melee the whole swarm of zombies (we even killed a tank using melee because he could not reach) but the attacks also knocked back the zombies. L4D placed a Fatigue system into play and after several attacks your next few got slower and slower (can't swing that lead pipe for an hour straight can you?)
As for a game becoming a parent, with its implied responsibilities, there are systems out there in effect already. The last computer I owned had it set up where I could set time limits and hours of use on user accounts for anyone under my level of authorization. If a game places this into effect I think would be one of the best options. "Little Johnny can only play on account 3, between the hours of 10am and 8 pm, Saturday and Sundays." but voluntary, no one should be forced to use the system or even be cut off if they play for extended periods.
Anyways, while people may agree or disagree with me or how the company sets up the games, that is my opinion.