for example: print "fox': would still run correctly! and print literally "fox".

Well, it isn't that hard to modify perl to allow that. Of course, as soon as you have a perl that allows that, you'll come crying "how do I print a sentence with a quote in it?", because if you write:

    print "O'Reilly";
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your perl is going to think the string ends after the O.

Besides, if you can use either quote, what's this going to print:

    my $value = 7;
    print "The value is $value';
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will it do interpolation or not? And how many terminating delimiters are you going to allow if you start a string with qq !?

Abigail