The idea is great but its really hard to do since the chips inside are so small... The pins on that phones are gigantic which if anyone were to design a phone with such huge pins, even a phone from 1980s would out perform it...
With that being said, there is a modular phone that is nearly complete to having its first prototype thanks to Motorola... I don't think its fully modular like in that video which imo, is impossible to have but this comes quite close to it by the looks of it
http://www.digitaltrends.com/mobile/motorolas-prototype-modular-phone-almost-ready/
http://phandroid.com/2013/10/29/motorola-project-ara/


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