I've talked with some of the Garmin folks about this, but wanted to post it on the forum as well.
We'd like to be able to store data that is acquired using the Muscle Oxygen profile on a Generic ANT channel in with the FIT file for the activity. The Muscle Oxygen profile has all of the specifications for the FIT data. This would be a major limitation in functionality for us if Generic ANT channel data can't be retrieved from the watch in FIT format.