Gutenberg Modify core taxonomy panel element via wp.hooks.addFilter

Because your plugin handles both hierarchical and non-hierarchical taxonomies, then I think it might be a better option to copy the HierarchicalTermSelector component, and return the copy from the CustomizeTaxonomySelector function.

And you can see how I did it here — Updated to use the JavaScript Build Setup which makes things like transpilation super easy.

The plugin (or the JavaScript stuff) is not perfect, but it should be good enough as a starting point. And you’d see something like these:

PS: In the demo, the category “Test” and tag “Test” share the same name, but they’re of a different taxonomy. And the same goes to the category “Test 2” and tag “Test 2”.