Apple “broke” the haptic feedback associated with invoking Siri, by “fixing” the problem that there had ever been any latency before. Have an iPhone 6s or 6s Plus? Go ahead, I dare you: hold down the home button and start talking to Siri. You will not escape its attention. It’s ready to go when you are, so it would be obnoxious of it to impose any contrived delay or to give taptic feedback that is uncalled for.
I just tried this out on an iPhone 6 vs. an iPhone 6s this morning. When you press the home button on the 6, Siri buzzes (that ‘ding’ is gone), and then there’s a slight pause. So sometimes, you’ll start speaking before she’s ‘listening’.
On the 6s, there’s no buzz, and Siri can never miss the start of what you’re saying.
Neat trick.