Creating a new transport protocol for use on the whole Internet is a massive undertaking, not only in purely technical terms, but much more difficult, in political terms. Getting all of the world's sysadmins to allow your new protocol is a massive massive undertaking.
And if you have the new protocol available today, with excellent implementations for Linux, Windows, BSD, MacOS, Apple iOS, and for F5, Cisco, etc routers done, it will still take an absolute minimum of 5-10 years until it starts becoming available on the wider Internet, and that is if people are desperate to adopt it. And the vast majority of the world will not use it for the next 20 years.
The time for updating hardware to allow and use new protocols is going to be a massive hurdle to anything like this. And the advantage to doing so over just using UDP would have to be monumental to justify such an effort.
The reality is that there will simply not be a new transport protocol used on the wide internet in our lifetimes. Trying to get one to happen is a pipe dream. Any attempts at replacing TCP will just use UDP.