Interesting change. I was looking into it for a while and thinking.
I truly believe that users won't need to do filtering by the text for multiple reasons:

1) the text within the hidden elements could be so big and so huge (it could be even another iframe) so that search will take forever
2) if there is lots of common text in hidden areas then the search can become completely useless. Imagine that every accordeon represents math sections: Addition, Subtraction, Logarithm, Square, etc. It is obvious that those headers have a high likelihood to appear in the hidden areas in every single section, which would make search completely useless if a poor user just wants to find 'Addition' tab in the sea of other math related accordeon tabs.
3) The search you want to add already exists and it is called Ctrl + F in the browser.

The bottom line for the accordeon was a need in a tool in AContent which would allow to show available courses and then user can dive into details of a particular one. So search would allow to find the course you need in the set of the offered ones. The same concept applies to any other user usecase involving our accordeon.

It is a nice thought of you, but outside of the use scope for this widget.