Rubout is just backspace. IMO having it next to the 'a' is a really good position; I rebind my Caps Lock key to Backspace on my machines. It's more convenient than the Sun-style "Control as Caps Lock" layout.
One of my favorite keyboards of all time had the spacebar split in two. Because I learned typing such that I always use the right thumb to press the spacebar, the left half of the spacebar made a very good backspace. I've often wished I could find more good keyboards like that.
I can only imagine the huge powers having a hyper key would give me ;-)
http://computing.fnal.gov/docs/products/xemacs/v21_1/xemacs....
Depending on your keyboard layout, the "Menu" key makes a good Hyper, and if you've set up Caps Lock as an extra Ctrl key, you can remap your left Ctrl key to something useful.
You can also separate Alt and Meta to different keys.
A quick emacs session will show you whether your new modifier keys are working as intended.
IIRC you can do similar for the (text-mode) Linux console as well.