I’m running 4.4.0RC1.
The RT::Extension::PreviewInSearch does work, in that it displays the ticket when you click on a row.
It displays the ticket above the search results, not below, so I’m guessing something in the (search results) page has changed in 4.4.
Also, it threw 404 errors in the JavaScript console for attachments (because I am using the external storage now).

I’m not trying to be a pain, just wanted you to know!
(I’m quite sure everyone is far more focused on getting the final release out the door, rather than looking at extensions!)