From a a developer perspective, this is a lot more complicated than I think people are considering. Looking at this purely from an objective standpoint, the amount of resources that would go into something like this is probably not worth the investment. Considering they specifically have options for temporarily allowing you to see the person and chat in instanced content means they've thought about this and have arrived at a solution they are currently satisfied with.

Having said that, I think there is more they can do, and I believe they've mentioned there is more to do in the future with friends list and what not, so I don't think they are done with this.