This was the way it worked up until the end of cata. And in cata the decline started. So these systems have little to do with WoW's success. And "business bullshit" is the only reason WoW still exists.
people want to be mindless dogs and bitch if they no life it and run out of content, tell them to deal with it. it all comes back to personal responsibility. you go out into the game, you pick what you want to do and you do it. you should have some form of comprehension that there will always be a limited amount of things to do. if you want to set some kind of limit so you feel like you always have things to do, that's your own prerogative.
Blizz can't tell them to deal with it, since they will just stop paying. The solution to this is to ditch the 1 month subscription option and only offer 3 months at a time. With this limitation your idea works decently. You just can't have the new content increase your characters powerlevel too much as that would break the balance of the game. And this wasn't even possible in vanilla as raids were limited and the only source of high-end equipment so no grinding your powerlevel there.
And with my suggestion you won't be limited. Maybe it should be worded differently, like exp. Think about this: Torghast will drop the legendary currency. This will be very very slow and tedious, like grinding reputation in classic (think of every legendary as a classic faction). BUT at the start of every weekly reset your legendary powerbar, which has normally the color yellow (or whatever will be used in SL), gets the color red. This works like the rested buff for exp but with factor 10. You grind X amount of legendary power, your powerbar will change to green and you will get 5 times as much power. But once you get X power again, it changes back to yellow and you get no bonus. You can still grind as much as you want, just without a bonus.i don't want to be limited by anything but the actual existence of content to consume. if i want to throw on a tabard and do dungeons till i feel like i want to die, that's what i want to do. that's the way it should be. i repeatedly face the fact that even places like 4chan lacks the amount of entertainment i need to consume to not feel bored. i would need an unending stream of lore being produced by the minute to not be bored, and that's never going to happen. caps will do nothing but piss me off and make me bored faster.
Does that sound better?