Thanks for your suggestion.
About stdlib, the idea is to let to people the management of this library (that is, you :-). We are just packing everything into the distributed jar file but we do not modify it.
Since stdlib is really open sourced, you can clone it from
https://github.com/plantuml/plantuml-stdlib and add some common-full.puml files that would include *all* existing icons (ok probably you are not going to manually create this file and write some script that automatically generates it).
I suggest that you create some new files common-full.puml rather than modify current common.puml file since this may break compatibility with existing diagrams.
Then you do a pull request and we integrate those new files into
https://github.com/plantuml/plantuml-stdlib and pack them in the jar file.
Does it sound good ?