IPv6

Well the spec was created in 1995 and the 6bone(tunnel based testing network created in 1996) was shutdown in 2006 due to the increase in native routing. That is IPv6 had a sufficient internet presence that the test network no longer felt necessary...and here we are almost 20 years later...soooooooooooo...yeahhhhhhh. Tbh IPv6 has existed for basically the entire existence of the wide spread use of the Internet yet it was never deployed back then.