Until PKIs are able to represent the rich diversity of trust relationships that exist in the real world, they are mere curiosities with marginal practical value.
PKIs are able to represent the blah blah blah; your software isn't yet translating that into something that you want to use.
It is not a software issue.
That you can construct a PK structure to represent a set of trust relationships for some purpose does not mean that there is some general purpose PKI.
There isn't.
That is, that you must construct a PK structure for every different purpose is not a software issue but an operational problem too complex and costly to be solvable.
Masataka Ohta
PK
Shared key cryptography with KDC, either, does not offer the general purpose infrastructure, though shared key structures are easier to maintain.