Attention: For those of you who just clicked this to quickly add /notsigned because you're grumpy so-and-so'; consider that it might actually be a half-decent money sink, as well as being a fun distraction from the monotony of every day GW grind.
On with the general idea:
@ - There should be a lengthy quest. To get married, a couple should have to acquire a gift each, a ring each and the proper dress, of course. (Perhaps more than just this, and probably class specific.)
@ - The quality of the ceremony should be determined by how much the two players are paying combined. The style should be determined by which land, or which of the six temples the ceremony is held in.
@ - There should be an island where only married couples can go, with unique items not unlike candy cane equipment. Just novelty stuff and side activities to flesh out the addition as a whole.
@ - Same sex marriage should obviously also be possible. I shouldn't even have to mention it, but a part of me knows that I do, so there it is.
@ - The six temples: These, like the island exclusively for married couples, would be smallish new areas accessible through the marriage ceremony. The six temples are comprised of one temple for the whole pantheon, and then one for each individual deity. No temple provides any specific blessing or benefit; it is purely about changing the style of the ceremony.
Extras:
There should be titles for people who repeatedly disband marriages, as well as for those who go unmarried for a year or more, ie; "Certified Bachelor“. This should also work in the reverse, although at the moment I can't think of a title for a long marriage that isn't awfully cheesy.

That's all I'm going to write for now. I'm prepared for an awful response, although I can't imagine why. This idea is not about augmenting PvE or PvP, but adding to those things shouldn't be *all* we look at.
~Mitsuki~