One of the biggest flaws WoD had is a long content drought, a content drought with very little additions 6.1 being laughably bad and 6.2 being very meh at best.
Legion has already been confirmed by blizzard to have more than 2 patches, which is why I believe they need to make it longer than every other expansion combined, by having regular updates nearly every 2 months.
Why Only 2 Months:
Because Blizzard doesnt really have the excuse, they are developing another expansion with Legion but at the same time they clearly have alot of people working on Legion itself, and content droughs are killing WoW's subs to the point of it never recovering from them.
Blizzard needs smaller updates again, patch content on a regular basis, if this game ends up being at 7.7 by the time it finally moves into expansion 8.0 I honestly would not mind at all.
Cant you just be content with launch content?:
Consumers go through launch now in less than a month at best, and by the time they get to raiding, something blizzard onpurposley held players back from doing at the launch of WoD, they go through it like a cheese grater.
So no, being content with launch content is a very pointless and niche argument. The playerbase needs to realize that theres more than one target audience blizzard has to please, and with patches like 3.1/2 and 5.2 it is clear that blizzard has in the past made grounds in trying to please them and knows very much that it is "capable" of doing so.
Blizzard needs an "Outlined" plan, one that gives us an idea of what to expect post launch.
Wouldnt knowing everything kill the hype?:
Just look at ESO and SWTOR for examples of how knowing everything can make a game better.
Devs constantly giving at least some kind of feedback at a regular basis gives people a reason to keep playing and know that the game is infact being loved and cared for by the team working on it.
A good game at launch just isnt good enough anymore, you need to think "ahead" of launch to be good, you need to be ready for the next month of content so that people are constantly kept Hooked to the content your offering at a regular basis.
GW2 prooved with its Season 1 and Season 2 format, that Patch content updates DEFINATLEY pay off, people will return to play the content, even if they go through it quickly, because they will have "things" to do. And for those that dont, they will wait till the full thing is done then return to have mountains of stuff to do.
There is a thousand reasons why patch content "is" better than having another expansion waiting 1 year for it with no updates. Even Ruby Sanctum as crap as it was, was something to fill the time between WOTLK and Cata, and was definatley what kept it from completley falling into stagnation.