If you think they're 2 iterations away from merging a seven year old, lightweight mobile OS, with what is referred to as "the most advanced OS in the world", that has over 30 years of code/history, and that magically all the input issues (mouse/keyboard combo vs. touch/tilt) will be solved by then...... ummmmmm, I'll have what you're smoking please! =P
Seriously. Just no. You have NOT thought it through in the slightest, beyond your personal desire to not buy multiple devices for multiple purposes. iOS and OS X will be seperate products (& rightly so!) for many, many, many years to come! Speaking as to your dream/prediction: the best you could realistically hope for in the next five years or so, is a "convertible OS" device. Say.... a fancy implementation of Fusion Drive in a MacBook, where the HDD is on the notebook & the flash memory is in the screen.... which is removable, & when removed, becomes a tablet, running iOS. Running the same OS is not probable, logical, or even feasible.