There *are* big networks that don't use TCP/IP. For example, in the context of IBM mainframes at large universities and research institutions, BITnet (The "Because It's Time" Network) emerged. This large worldwide network does not use the Internet protocol. BITnet can be reached from the Internet through special translators called gateways, but it is definitely a different network. Occasionally one encounters problems that can be traced to this fact.
<Section 2.3> The Future of the Internet
The future of any technology is difficult to forcast, and I do not profess to know what the future holds for the Internet. Some predictions that various forcasters have made for internetworking (and telecommunications in general) are:
o A proposal for a data "superhighway" called the NREN (National Research and Education Network) will pass the U.S. Congress. This is an upgrade for the Internet.
o Commercial use of the Internet will become more common and new schemes for charging for its use will emerge.
o The Internet will be handed by the government over to AT&T and the other "telecoms", who will charge so much to access it that the whole scheme will collapse.
o Optical Fiber will replace Coaxial Cable (Ethernet protocol) as the most common standard for LANs.
o The Internet will enter the home over ordinary phone lines.
o The Internet will enter the home over existing Cable TV coaxial cable.
o The Internet will enter the home through newly strung optical fiber as part of a unified system for Telephony, Cable TV, and the data communication, using [insert your favorite protocol here] as a standard.