I can't offer any assurance as to whether we're doing this or not, but I've been having some talks about it lately. There's less concern in how much time or difficulty there would be in implementing an offline mode, and more in the holistic considerations of what value it would bring.
As I've personally read through this thread (And others like it), there seem to be two camps of people: Those who, at times, aren't feeling social and just want more control over who can interact with them, and those who feel annoyed at all of the notifications (buddy invites, game invites, etc) they sometimes receive. Implementing an offline mode to please both of these camps isn't necessarily the best solution, because it wouldn't give users the control to solve only one of these problems.
In other words, all of these discussions about offline mode have revealed additional things that would have to be done in order to achieve the optimal solution (For example, an improved buddy list or notification system). Several solutions are currently on the table, and we want to be sure that in solving one problem for one group of people, we don't create a problem for another. At the same time, we also want to be sure that adding the ability to appear offline won't harm the community in any way (For a fun mental trip, think of what it'd be like if everybody was using offline mode )
Sorry if this post doesn't have the affirmations you were looking for, but I assure you that this request hasn't been lost on us. Thank you for being patient.