Fedora already supports booting from a USB device but it then mounts that device so it can not be removed. Since my USB drive is only used for booting I remove it as soon as the computer is booted. I was wondering if this could be built into Fedora. Currently I have two boot partitions. One on my USB drive which is kept on my person for security reasons. The second is on my LUKS encrypted hard drive partition. Since I can not (for obvious reasons) boot off a encrypted partition I boot off the USB drive but I mount the boot partition on the encrypted drive. This allows me to remove my USB drive. The only gotcha is to keep the two boot partitions in sync which I do manually. I added a rule to /etc/udev/rules.d that when my bootable USB is connected it will sync the two boot partitions. This syncing could be automatically done at boot time after the encrypted boot partition is mounted but I have not looked into that.
This isn't something that we're going to support out of the box as there are too many ways it can fail if someone doesn't have their usb key plugged in at the right time.