No, no, no, no, no.
Do you really think all of those software engineers went to the trouble of developing iOS to junk it five years later after a crapload of success? Um, no. They took core elements of OS X and tweaked it for a touchscreen mobile platform. You start running a desktop OS and every little thing is going to be affected, which means MOUNDS O' BLOAT. I don't know exactly how much room OS X takes up, but the system software for the MacBook Air comes on a 2GB flash drive. iOS takes up a tiny percentage of that.
Now let's move on to hardware. Mac OS X Snow Leopard requires an Intel CPU. Putting aside the difference between an Intel CPU and A4/A5, the slowest Intel CPU on a Mac is about 1.2 or 1.4 Ghz. The current iPad and iPhone CPU is about 1 Ghz. Hello, sluggish. Also while looking that info up, Mac OS X requires 5GB of disk space. So my 2GB number was severely low-balled. That doesn't even address GPU issues or RAM (minimum 1GB for OS X, less than what any iOS device has).
Now let's talk battery life. You can thank computer-optimized batteries and plugs for me being able to type this long on my desktop. OS X is not optimized for the lesser computing ability of mobile devices, so it's going to run the device hotter and burn right through that battery.
I'm not trying to totally kill the OP's excitement, but I am trying to totally kill this notion. iOS was designed for mobile devices. Apple just made $6 billion profit last quarter. Buyers have spoken and say Apple is doing just fine. Future iOS versions will probably add more features that I guess you like from OS X, but a full desktop OS is overkill on a mobile device and mostly waste.