If you only want to move to the next line if you are at the beginning or the end of the line, I guess it works. For any other navigation, your cursor jumps to a random position. I just tried this, and for any line longer than about 3 characters, "next-line" becomes "random position on the next line". Not useful.

Other problems include lining up similar constructs:

    my $foo = Foo->new(
        bar  => 'baz',
        quux => 42,
    );

With a non-monospaced font, there may not be an integer number of spaces that would allow you to align things.

Using a proportional font for programming seems like using a railgun to put a square peg through a round hole. Sure, you can do it, but why not just get a round peg?