Its always an interesting thought experiment to see how much of what we do with modern systems can fundamentally be done with 30yr old tech. Instead of HTTP and the Web there was Telnet or 3270 which fulfilled much of the same goals as an application delivery platform. Graphics would be right out but the core functionality of apps like Twitter, Facebook, GMail, word processing and office apps etc. could be done on 30yr old systems. Maybe the biggest problem would not be functionality but scale, no system of the day could scale to the many millions of active users that current systems support, AFAIK.