that should be a place that is accessible to all users in any scenario (system, perlbrew, etc) who may run the module in a cross platform compliant manner; and that the module can write to. Is there even such a place?

That sounds more or less like a place where "everyone" can write to. Being a systems admin at my employer's, I can tell you sysadmins don't like such places.

I think the most reasonable approach would be to explicitly ask (e.g. via Parameter) for the place to store this info, so that the users would then forward this to their sysadmin who then could set up a place readable to all, and schedule an update job (e.g. monthly, or some schedule to be suggested by you)