That doesn't solve the problem that bash is completely useless for manipulating JSON.
It certainly would make writing Python scripts that need to interact with other programs easier. But Python doesn't desperately NEED to interact with so many other programs for such simple tasks like enumerating files or making http requests or parsing json, the way bash does.
Then you have to install the new version of bash on every system you depend on json parsing, negating the argument that bash is installed everywhere.
If bash was ever actually going to get json parsing in reality, it should have done that two decades ago like all the other scripting languages, since JSON is 23 years old. So don't hold your breath.
It certainly would make writing Python scripts that need to interact with other programs easier. But Python doesn't desperately NEED to interact with so many other programs for such simple tasks like enumerating files or making http requests or parsing json, the way bash does.