@paul.moore - thanks for the comment.

I am trying to work from both https://packaging.python.org/specifications/platform-compatibility-tags/ which describes in a few words the goals of PEP425.

As to the PEP425 itself, it does not specify what a tag looks like. Within the EPE the only description is:

The platform tag is simply distutils.util.get_platform() with all hyphens - and periods . replaced with underscore _.

Like the platform-compatibility-tags reference says - the rational (aka requirement) 

"distributions should have a file naming convention that includes enough information to decide whether or not a particular archive is compatible with a particular implementation."

The tag I am proposing 'includes enough information'.

Further, as to the comparison of Linux and macos approaches to tags and deciding "whether or not a particular archive is compatible" AIX system architecture does not have to deal with the diversity that Linux platforms do - so it would be closer to macos approach.

Actually, deciding if a bdist is compatible or not will not be the hard part. However, I prefer to discuss that after a starting point - the platform tag itself - is achieved.

The last bit I am looking into is how, e.g., ``pip`` looks/searches pypi for candidates.