First off, the goofy weapons are not placeholders. They're real, and awesome.
Second off the physical damage mitigation from a shield is a pretty pitiful contribution compared to the weapon being a large int/sp upgrade so if it is, I'd imagine a lot of shaman and paladins will be taking it.
The amount of SP and INT on the 2H mace is going to be the same as the amount of SP and INT on a main hand/shield combination of the same ilvl. It might be something that paladins and shaman would take temporarily, but it's definitely not going to be BiS (BiS appears to be the fist weapon).
As far as the shield vs 2 hander argument, using a shield is about a 13% physical damage mitigation increase. That is pretty insignificant, and you have to take into account that there are two types of physical damage you will take in a raid (1) an add or boss not being picked up. In this case, you are likely to be 1 shot with or without 13% extra armor mitigation (2) raid wide physical damage effects. It's the raid wide physical damage that you would want to take into account. If they make another raid like Heart of Fear with almost all physical raid damage it's something to be concerned about, but most raid damage is spell damage.
For T14, I think the staff is actually BiS for Shaman (or at least basically tied with the mace) because
(1) There is no 509 shield (or off hand without hit on it)
(2) You can VP upgrade two slots at once with the mace, effectively getting ilvl 517 in both slots instead of an ilvl 517 main hand/ilvl 502 shield. The higher ilvl offsets the lack of Spirit itemization
(3) You won't (or at least should not) likely VP upgrade a 502 shield. The stat itemization on shields and offhands is so small, and it's a 502 item to begin with, so it would likely be your lowest priority item to upgrade, and you probably won't get to that point before 5.2 goes live.