I agree with NYguy, looking at the last pic he posted, a taller, thinner 2WTC would look great in that spot. With the Nordstrom tower possibly taking the title of America's tallest tower, this is a chance for 2WTC to quickly get the title back.
If I was in charge of redesigning 2WTC, I would combine the original Libeskind design for tower 1 with what we have slated for 2WTC. I would raise the height to 1500 ft, then I would add a mast like the Libeskind design had, with a glass atrium that would pump fresh air into the tower. Here's a pic of what Libeskind's original tower was supposed to look like. Notice, it has a similar roof to what 2WTC is supposed to have.
Raising the total height to coincide with the completion date of all the buildings, let's say 2021 feet, would be very symbolic.