@PhilipDAth You're fast! I was just coming here to post when I saw your message. There's been a bit of a delay getting the information on the devnet site, but it should be updated here shortly. In the meantime, here's the information I do have for you.
Full Frame snapshots require MV 4.2 beta firmware
It is only available via the API; not using the screenshot option within the dashboard.
It is only available on live video - which is how it can be done at the full 4MP sensor resolution, and not the configured settings for video.
The API call should look something like this: