Another approach to handling this, and other, issues is to allow options to EnumMeta.  My original aenum code had the default Enum class as unordered, no duplicates allowed, non-indexable, etc., but then allowed options to be passed in such as DUPLICATES to allow duplicates, ORDERED to add the ge-gt-le-lt methods, INDEXED to add __index__, etc.

For the aliasing issue this method is more robust as placeholders are not required, and code like this will work:

class Physics(Enum):
    e = 2.81847
    pi = 3.141596
    tau = 2 * pi

To make that code work with placeholders is possible (I have it in aenum) but a major pain (I was about to remove it before my offer to help with ref435 was accepted).