Well there's no character customization at all, so basically the whole char is the gear its wearing, so this trading was not needed at all. Later they added Plvls, which now make the only difference and what the character trading would be all about at this point. Next patch some BoA items will apear so yeah that's the point character trading would make any sense (as long as BoA items would become actually character bound during the trade).
Like some other things that they planned for post-release most of these have likely been postponed until the game gets into a state in which the majority of the audience is sufficiently satisfied before returning to them.
Easy add for an expansion. And Enchantress, and traits, and charms, and blah, and blah...
This is always a cool argument. Why not instead of postponing these didn't they postpone monster power, uber bosses and paragon leveling? People say the things you mentioned are already done anyway. Why keep something that is done but develop _new_ things. Why not develop the new things for an expansion?
Because it's easy to say "yeah, they had those finished and now they're just keeping them for an expansion for easy money", but meanwhile they develop different things. I don't know which software developer would bring such logic.
Doesn't matter though. When the things you mentioned get put into an expansion anyway (because they've been through heavy iteration but hey, who cares, they were likely "done" pre-release), people would just say "see? told ya they're just keeping them". Ah, the joys of argumentation.