Like all of the best religious ideas, it is one that came about by a man faced with his own mortality.
On a side note, and this is opening a huge philosophical can of worms, I'm not convinced of the utility in merging our intelligence to machine intelligence in such a scenario, either from the point of view of overall utility (what do they gain from our meeker intelligence?) or from the point of view of our own "existence" actually being near-immortalized.
Stated simply, if you could make a perfect copy of my brain into a 20 year old clone of myself (I'm 39) and that clone were created such that it didn't have to worry about issues like telomere shortening or any of the other processes theorized to cause issues for clones, but after the process was completed the original copy of me would be terminated, I wouldn't take that deal and I doubt many other people would either regardless of how they feel about the theoretical ability to duplicate an exact copy of their own consciousness. Ultimately, the copy of me that is me wants to continue on but cannot.
I will die.