I'd love to have this option!
There are pros and cons here, but I vote for this option so who wants it and believes it has advantage can use it, the other may skip it, but for those that are stuck to laptops and are limited with amount of RAM this means a lot, especially during crash as it will use pagefile, and when you're stuck with slow HDD and are forced to use pagefile this is very important feature. mikesw explained various cases when this doesn't fully work, but those are exceptions and can't be handled, but that doesn't mean that this one wouldn't help.
Even if PF grows, after restart it will be reduced to its default value which will remain defragged at the begining of the HDD.
I would also like to see an option to add other files/folder in a specific order to the start/end of the disk.