I think the point he is making is that the industry first went with a 10g single link, and then 40g over 4 links. Then they figured out how to do 25g over a single link, and 100g over 4 links. Those 25g/100g are common for enterprise switches. It might be fairer to say 40g is dead, 10g still has use cases.
Edit to add: If you want an example, these are the NVidia ConnectX nics available from FS.com, the lowest end one is 25g, then 100g, 200g etc.