The question should not be 'will it be supported', the question should be: 'do you want to use it'?

It's a real global variable, it lives in the main/default symbol table, you can not lexicalize it, and more important, every file and package can modify it.

Especially the last point will make it hard to maintain and/or modify and/or integrate it with other programs.

This is ofcourse all true for $_ and @_, but do you really rely on them having a certain value? I certainly do not.

Also note that there is no point to have a 'default' hash. You can create a package-global hash (%config for example) which you can access from other packages by including the package name. And if you are not happy with that then you can even import it in other packages.