A few weeks ago, it became clear that G0ogle+ is headed toward a pretty major overhaul to the post editor that would bring support for new formatting and styling options for text. The latest update brings clues that this isn't where the new features will stop. It looks like Google+ may also add separate titles to posts and also integrate with Google Drive for attachments and that will include previews.
Disclaimer: Teardowns are based on evidence found inside of apks (Android's application package) and are necessarily speculative and usually based on incomplete information. It's possible that the guesses made here are wrong or inaccurate. Even when predictions are correct, there is always a chance that products could change or may be canceled. Much like rumors, nothing is certain until it's officially announced and released.
The features discussed below are probably not live yet, or may only be live for a small percentage of users. Unless stated otherwise, don't expect to see these features if you install the apk. All screenshots and images are real unless otherwise stated, and images are only altered to remove personal information.
If you look through long-form posts on G+ these days, most people have adopted the practice of writing their titles in bold to give them a little more visibility. In much the same way that Twitter ultimately implemented retweets and replies after they became commonplace practices, Google appears to be adding a dedicated title field so authors won't have to screw around with formatting to make them visually distinct.
Titles are optional, so you don't have to add one if you don't want to. There seems to be a hard limit of 140 characters for titles. (I've got a feeling that's a subtle poke at Twitter.)
As for how the title will look, there's not a lot to go on yet, but the style currently in use appears to merely mark the text up in bold. But remember, that can and probably will change when this feature is rolled out. It's also possible titles will be given more visual separation in other ways.
Attachments and previews
Several versions ago, Google+ gained a few new lines of text that referenced adding files from Google Drive. At the time, I suspected those lines may have tagged along with a code library that had been used for accessing photos. This is fairly common. However, two new lines were added with the latest update that are far more specific and all but confirm Google+ will support file attachments directly from your Drive cloud storage.
Obviously, we can already create posts with links to Drive, so what makes this different? Simple answer: Drive attachments will include a preview of the file. Anybody with permission to see the post will be able to see the name of the attached file plus a thumbnail preview of its contents.
<string name="dialog_title_drive_picker_launch_notice">Be careful when posting Drive files</string>
<string name="dialog_body_drive_picker_launch_notice">Anyone who can see your post will see a preview of Drive files, even if they cant access the file itself. That preview includes the title and a thumbnail.</string>
<string name="drive_picker_title">Share a Drive item</string>
<string name="menu_view_on_drive">View on Drive</string>
<string name="sharebox_drive_content_description">Add a file from Google Drive</string>
It's important to note that people may have permission on Google+ to see a post with a Drive attachment, but they may not have permission to access the file on Google Drive. And as the text points out, those people will still be able to see the title and image preview, even if they can't access the file. As usual, you'll want to be careful attaching anything in Google+ if it's not meant to be seen by the general public.
The APK is signed by Google and upgrades your existing app. The cryptographic signature guarantees that the file is safe to install and was not tampered with in any way. Rather than wait for Google to push this download to your devices, which can take days, download and install it just like any other APK.