This is assuming that the internet WILL definitely evolve exponentially. Does Moore's law apply to the internet as well? Can people really get bored with it in 20 years? It doesn't seem so science fiction to assume that something different and better that we haven't even dreamt up yet will replace the internet making it entirely obsolete or pointless to use.
Make it out of whatever you want, wires, lasers, moon beams, the internet is still the internet. A global system of interconnected computer networks.
It's not internal.
Define internal. If the internet fails our economy is in serious trouble. Thankfully we still have radio and telephones for communication.