I think that plan may have been axed, as (anecdotally) the number of communal mailboxes seems to be relatively low among the few cities I've visited/lived in over the past couple of years. Also anecdotally, I'm not sure why the majority of houses (in the burbs) seem to have a mailbox by the door or a mail slot instead of box by the curb. They definitely exist, but feel like a minority outside of rural areas.