Well, it could be simple as build up a regular linux install (set as regular user things such as: default applications, ppa, driver, wallpaper/themes etc); then backup the whole disk (all the partitions inside) into a single downlodable package.
Then, user may only need to do something like
gunzip -c ~/Download/ItchOS.img.gz | dd of=/dev/sd[usbkey letter]
to "install" the system onto a usb.
But there's no doubt that website and app should have aboslute priority.