That seems weird, I don't really see any point in it.
If the dock is a whole computer with an ability to dock a laptop, it's kinda weird because you can only use one of them at the same time. It's like having a desktop computer and then unplugging all peripherals and replugging them into your laptop - why would you do that on a regular basis? In my experience, dock users usually have powerful laptops and use them as primary systems and docks just provide them with easily available extensions.
On the other hand, if it's just a monitor, it's awkward because you can only use that single Apple display, they don't give you any choices.
I'd prefer they just release a regular dock - not having one is currently a major downside of their laptop range.