I've not seen anything about this in the preview SDKs for 4.0.  If this did come in 4.0, it would only be on devices with 4,0, and last I heard 4,0 wouldn't be back ported to current devices, but only be available on new devices.

What gyro data are you looking for? We already expose accelerometer and magnetometer data in Sensor.Info since ConnectIQ 1.2.0 and high frequency accelerometer data via Sensor.registerSensorDataListener() since ConnectIQ 2.3.0.

I'm after the gyroscopic data so that I can record attitude controls. I want my watch app to be able to calculate kitesurfing jump height as many of other product such as ( WOO or PIC ) do. GPS and BARO altitude are simply not accurate enough. The accelerometer data is great but there are too many degrees of freedom in  a jump and the kite provides extra acceleration that is off axis to gravity and magnifies it so I need a gyro reference. With a gyro reference I can resolve the vertical component of acceleration, and calculate the an accurate vertical jump height. Magnetometer also useless thanks to the proximity of metal objects when jumping skewing the fields. I would use a filtered trigger being when gravity exceeds a certain value over a certain time, then stop most other watch functions and record the Net G force and the gyro values at higher update rate as possible, then stop recording when a G force event happens. After that, do the maths on the watch for a few seconds, store the jump height somewhere and wipe the recorded gyro/net g force.

If you're looking to measure acceleration (g), then you want the high frequency accelerometer data mentioned previously.

I do, but the information is useless by itself because when a kitesurfer jumps, the watch experiences more than 1xG, and the G is not vertically straight up either, and it moves as the jump continues. So looking purely at the accelerometer values, it is then impossible to tell how much of that acceleration is vertical, and how much is horizontal - if I used the max net acceleration  ( which if you assume is straight up, it will always give incorrect answers. )

By using the acceleration values, and watch orientation ( gyro readings ) - you can fairly easily figure out what the vertical component of acceleration is, which is all you need to figure out jump height - so you need both accelerometer readings and gyro data ( unavailable at present ) 

So this is probably a stupid question on my part, but can you use the accel data from just before the jump to set a baseline vector/plane for horizontal motion, then use that to determine the vertical component of the jump? (Of course that assumes that the orientation of the watch doesn't change too much during the jump.)

That is the problem, the watch position changes just before the jump, during the jump, and just before the landing, as does the acceleration vector which is up and downwind, up then up and downwind again. I am sure there are other sports / workouts that could benefit from having the gyro data enabled and not just in this case to monitor rotation / form. If your a pilot of any description having a backup HUD  on your watch that displays horizon data could be a life saver.. plenty of applications

The 4.1.0-beta1 SDK has gyro data.  It will only be on the system 5 devices, and no devices have that firmware yet:

Class: Toybox.Sensor.GyroscopeData

Overview

I see you've posted the link to that page elsewhere, but every time I try to click it, I get a page not found error. Am I pointing to the wrong version of the API doc? 

Also, I'm new to development for Garmin, what is a system 5 device? I have a Forerunner 945 that I'm trying to make my app for. What version is that? and when can I expect to see a firmware update to "system 5"?

Thanks.