MOXY recently released a second IQ Connect Data field for the Garmin environment.
You might, for example, want to see left and right leg oxygenation values. Probably not so useful for most of us but the sports science world will no doubt appreciate the possibilities of multiple measuring positions.
MOXY also confirmed the inclusion of MOXY data into FIT files produced by the WAHOO Elemnt.
I think I am correct in saying that only data from one sensor will be recorded at present into a FIT file.