The front will likely remain flat, though, resembling the good old iPhone 5C. So a smoother transition between the side frame of the phone and the back glass is expected. A more comfortable grip is likely the goal and the titanium build will probably reduce weight. The tipster does say that it's too early to confirm the changes and even if there's an internal debate at Apple, nothing is final.
Then again, this prediction isn't too far-fetched since Apple's MacBook and Mac mini feature similar looks, so the design language may trickle down to iPhones too.