Since WP7.5 devices can't upgrade to WP8, and are instead limited to updating to version 7.8, what does that update contain? Are any of the new features in Windows Phone 8 be included?
According to winsupersite.com
The Windows Phone 7.8 Starts screen will be changed to look like that of Windows Phone 8. It will fill the entry screen with tiles, and not leave a strange “white space” gutter on the right side, as does Windows Phone 7.x. (This was apparently the source of some great number of user complaints, the theme being that Windows Phone doesn’t completely take advantage of its onscreen real estate. Commoners.)
Windows Phone 7.8 will now support three tile sizes, just like Windows Phone 8, and not two like the current version. And apps can be written to support any of the three sizes, giving the user the ability to choose between them (as is done with Windows 8’s live tiles). In addition to the current Small (square) and Large (rectangular) sizes, Windows Phone 7.8 and 8 will also support a new Smaller size, which is a fingertip-sized square that is one-fourth the size of a small Tile. Mix and match as you please.
Windows Phone 7.8 will be delivered directly to all Windows Phone users, bypassing the carriers. You will be able to download and install Windows Phone 7.8 over Wi-Fi, at home or wherever else, and install this update. This type of updating will be made available in Windows Phone 8.