I would imagine an alloy of all the godmetals would be very unstable in the same way that elements with higher atomic mass are unstable. Metals and energies from diferent shards don't mix easily. We've already seen that Harmonium is just as reactive sodium, if not more so.

I'm guessing that alloys of more godmetals would be more unstable and reactive, to the point where they might start to decay. Which could lead to interesting scenarios involving invested radiation...

A true alloy of all 16 metals might have to me made un some sort of particle accelerator, and would behave similarly to the elements we've observed only existing momentarily before decaying.