The proposal for "IPng" that became IPv6 was selected in August 1994. It and various other proposed protocols had been under discussion in the IETF for roughly the previous two years (from memory). Prior to that the IPv4 address exhaustion issue was certainly known about. For example OSI CLNS had (has?) variable length addresses and was for a while a contender for IPng. NAT actually extended the lifetime of IPv4 by decades. In 1994 we were forecasting the end of IPv4 with the introduction of Windows95! Conversely, the biggest benefit IPv6 brings today is avoidance of NAT.
