That was my first thought, and the following seem to be assuming that companies will decide to change their policy. But many public WiFi block UDP traffic, are they going to change their policy? Are the people in charge of it even aware about it? (Think coffee shops, restaurants, hotels, ...) Are we going to have websites supporting legacy protocols ("virtually forever") in order to build a highly available internet?
Also, ISPs in some countries have not been UDP-friendly. I'm thinking about China mainly, where UDP traffic if being throttled and often blocked (connection shutdown) if the volume of traffic is consequent - I assume they apply this policy to block fast VPNs. Are they going to change their policy? Worst scenario here, would be to see a new http-like protocol coming out in China, resulting in an even larger segmentation of the internet