Hi @sudohuman and thanks for your query. Mixer unfortunately doesn’t support overlay extensions at the moment but it’s definitely something that would be great in the future. Please petition them on their own site with our support!
As a possible workaround, you can also stream gaze to Mixer by burning in gaze overlay in Open Broadcaster Software (OBS) although it won’t be possible to toggle it on and off on the viewer side though.
If you are interested, you can read further information about Tobii Ghost @ https://help.tobii.com/hc/en-us/articles/210245345-Show-off-your-gaming-skills-with-Tobii-Ghost-Streaming-Gaze-Overlay-