> Is there a reason for calling `object.__new__(cls)` rather than `cls.__new__(cls)` or `DimCoord.__new__(cls)`?

There's no particular reason for using `object.__new__(cls)` except `object` is (currently) the only class in the MRO which defines `__new__`. That  said, it would be better as either `Coord.__new__(cls)` or `super(DimCoord, cls).__new__()` to allow for the subsequent addition of `Coord.__new__`. Currently we mostly use the `Coord....` form elsewhere so I would suggest we stick with that.

>...or even just DimCoord(...) at the bottom?

As stated by @esc24, avoiding the constructor is the whole point of this PR :wink: 

> `cls` will be `DimCoord` at runtime.

True ... unless someone had defined a subclass of `DimCoord`.