Dan

Gymconnect / Gem Retro is a good solution where compatible but Nordictrack uses a proprietary serial maintenance port. It's not csafe.

There is already a solution on github to control your ifit based treadmills and there is already IOS and android apps that can send data to zwift using ble. It would seem possible those two could be married. Unfortunately the zwift api is now closed.

Quite annoying considering all the hardware is in place and most likely software as well but locked away to keep loyalties towards ifit. Understandable but annoying.