Key/Keyring combo is all too easy
ideaconnection.com
ideaconnection.com
In programming, this would be an example of bad design.
http://en.wikipedia.org/wiki/Separation_of_concerns
In combining the key and ring into one object you make it so that the key+ring doesn't act the same as another key. You can't remove the key+ring or you leave the other keys without a ring. You have to make sure you have a single key+ring (unless you want to make them into a chain), if you get rid of one key+ring you have to convert one of your other keys into a key+ring to take its place.
Still, not an inherently terrible idea.
On the downside, how do you remove a key from the ring without the other keys getting in the way? Wouldn't the fixed key get in the way of being able to slide other keys aside?
Is there a topologist in the house?
The reason for the flat surface on current keys is so you can hold it steady while turning. A flat surface is ideal for this, a keyring, not so much.