Just downloaded the beta, however new functions of iMessage mentioned and demonstrated at WWDC don't seem to be available. I'm specifically referring to the invisible ink feature and the full screen animations. Is there a specific setting that I overlooked? Or is it just not available in this beta version?
You 3D Touch on the send button to access them, not sure how it works on an older phone, I'd try a long press.
To do the hand writing you have to rotate the phone to landscape, took me a while to figure that one out.