I think that's an interesting idea, but I can see where it might not work when you expect it to. Much like UNIVERSAL::isa, some people may call UNIVERSAL::can directly as a static method so as to avoid having to check if something is an object or package name. Contrived example:

sub has_method {
    my ( $target, $method ) = @_;
    return UNIVERSAL::can( $target, $method) ? 1 : 0;
}
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How often this will occur is hard to say, but it's at least worth a warning in the documentation. Whether it's advisable is entirely another issue -- I generally tend to think that one should realize that modules might override UNIVERSAL functions for a reason and respect that.