If it's not there to enhance game play, I can't see the point,.What stats would it give us? how would it make our chars' any better? The use of drugs in Identity is a good example of that, they've not just included them for the sake of it, drugs will effect game play, and our chars' via buffs/de-buffs....there is a point to it. Including marriage makes sense for role play, whether or not our chars' will actually benefit from it remains to be seen.
Relationship arcs in char' development has not, until recently, played a substantial role in gaming. Identity claims to be changing what it means to be an mmo, and this is one area it could do that for sure.