Form inputs change dynamically depending on number of options

In our style guide we have the following guidance on form inputs (single select).
1 to 6 options use radio buttons
7 to 15 options use a dropdown
16 or more options use a search select (select2).

This is straight forward on forms with no branching or dynamic input changes. I wanted to get views on how this feels when a selection changes the number of options and therefore the form input. Has anyone done anything like this before? Seen it anywhere before?

I will carry out a usability study on this form, however the developers are looking for some UX research on this and I’m struggling to find anything.

I have attached an animated gif as an example of a changing input (hope it works).
form-inputs