The iPhone could be a Thread border router, but it probably shouldn’t be
The iPhone could control Thread smart home devices faster
Thread could replace Bluetooth as a way to connect peripherals like the Apple Watch to your iPhone
Thread would be fine for most smartwatch uses but not for audio streaming
Thread might just be a bonus radio
Yes, it’s basically a new standard that sits next to WiFi and Bluetooth. All three have strengths and weaknesses for different applications.