Where Are IPv3 and IPv5?

The articles have paragraphes entitled "IPv0", "IPv1" and "IPv2". So not only it's not forgotten, there is actually an answer in the article. Don't hesitate to skim it before commenting.

To answer your question, IPv0 and IPv1 were part of TCP and IPv2 is the first draft for the split which was never used. IPv3 is a modification of the internet header but still in TCP. IPv4 is where the split happen. IPv5 is a streaming extension which was abandoned in favor of UDP streaming.