how about in Perl 6 being able to use require or a variant of use to be able to specify which of two versions of a given module you have to use in the script.
This already exists in Perl 5.
perldoc -f use
=item use Module VERSION LIST
If the VERSION argument is present between Module and LIST, then the
C<use> will call the VERSION method in class Module with the given
version as an argument. The default VERSION method, inherited from
the Universal class, croaks if the given version is larger than the
value of the variable C<$Module::VERSION>. (Note that there is not
a comma after VERSION!)
Tony