Perhaps I'm missing the use case for not wanting the search text to be updated.
Well, I also personally don't see a use case for it, but on the other side, I don't see that many users complained. Also there must be a reason why the search phrase is (seems intentionally?) not updated in the current version. People have different ways of working. And since the users are used with that current behaviour - for which we don't see a reason yet -, I think it is not bad to let them fallback to the old behaviour using the hidden preference. That is the only reason for the hidden preference.