I wouldn't mind an iOS-type OS on an iMac as long as it had some more features of a full-fledged desktop OS. As in:
-Multiple Users
-Printing
-Some kind of file system
-More apps of a creative side (ie movie editing, word processing, programming, etc.) instead of just media consuming apps
Note: this list is not exhaustive; there are many more features I'd like that I just can't think of at the moment.
Plus, some games/apps will need to be done, specifically those that need the accelerometers. I don't think people would want to swing around a 20/30 pound computer. But that would be a good way to make more money; people keep breaking them so they'll have to pay for repairs/new ones.
I doubt 10.7 will be such an overhaul. Probably more like Mac OS X 11.0 or a totally new naming scheme.