Had this idea 2 years ago when I got me the Sony SmartWatch 2 that has NFC,here in the Netherlands we pay with NFC cards for public transport,waited for an app that I could pay with the watch.
It appears that the watch does not reply on battery or internet access to use NFC for mobile payment. If true, this is a real winner. Problem with Apple Pay, Samsung Pay or Android Pay is that if the phone runs out of battery, then it is useless and you better have the wallet and your credit card on hand to pay for stuff. This swatch will work just as fine with or without battery.
Personally I only want 2 features in a smartwatch, NFC for mobile payment and GPS for SOS tracking. I don't care all those other features like heartbeat monitoring, blah blah blah.