"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
iPhone 4 Drop Test with Bumper Case Shows Little Protection
We've have known for a little while now that iPhone 4 bumpers do not offer all of the protection needed because customers have called in an told us. Although it does not take a video by iFixyouri to inform you that dropping your new iPhone 4 on concrete is a bad idea, hopefully this video squashed any doubts as to the bumpers effectiveness.
The iPhone 4 was dropped from a natural standing height onto concrete. The iPhone 4 with bumper lasted only 3 drops before the front glass cracked. This was the same number of drops that it took to break an unprotected iPhone 4. It does appear the iPhone 4 hit the concrete face down for the last fall, so how it falls likely affects the chances of the glass breaking.
Unfortunately, there have been no comparison tests with more traditional cases, so we're not yet sure how much better protection a full case actually offers.