I've thought about doing this, too. My cats are obsessed with the bathroom. Unfortunately, this might prevent me from training them, since you must keep the lid up.
Right now, my one likes to sneak behind me before I flush and grab the wet paper out of the bowl and run off with it. Any time I forget to close the lid, (and if it's yellow and mellow) I may end up with dried toilet paper chunks in my bedroom the next day. Gross!
At my mom's old work (a vet) a lady adopted a cat and soon after noticed her children weren't flushing their #2. The kids denied it, and then she realized that whoever owned the cat before had trained it to use the toilet!