Here's what Google had to say on the announcement:
"We've gotten very positive feedback from those of you testing it out -- such as this note: "The Gmail results feature is awesome! The fact that it's all integrated into one screen is huge." Many testers have requested being able to find Drive files as well -- as one of you put it, "It would be awesome if I could search my Google Drive from Google search as well :)".
"So starting today, you can sign up for a new and expanded field trial that makes it easier to find your stuff across Google, whether you're searching on Google.com or searching in Gmail."
Google claims to have been working on many features for this new trial such as improvements to search in Gmail, displaying results from Gmail and Google Drive while searching Google.com and other additional related features and improvements.
Improvements to search in Gmail include the ability to view relevant emails as well as results from Google Drive, Google Calendar and more when you type a search in Gmail. Personal search options on Google.com can be expanded through the trial, bringing in documents, spreadsheets and other files from Google Drive into search results.
You can sign-up immediately for the new expanded field trial. Once you do, you shall receive a confirmation email from Google when your account is ready. A quick reminder from Google mentions that "this trial is only accessible in English and for @gmail.com addresses (not available on Google Apps accounts). Also the experiment may not be activated for everyone.