There's a new 360° project property which adds a 360° option to the preview (which then can be turned on and off in the preview window and enables the preview to mouse-drag the camera angle) and which will add 360° meta data to the output if supported by the output media.
Also there is a new 360° stitching FX with several adjustments I can't further describe due to the lack of my experiences with 360° video editing. Same for the new "Scene Rotation" FX which seems to be made for 360° video and which offers stereoscopic options.

Is there a list of supported cameras for the stitching fx?

The stitching fx offers a modell list which contains Samsung Gear 360°, LG 360° Cam, Ricoh Teta V, Ricoh Teta 5, Ricoh Teta S and Ricoh Teta. There are differences in up to 6 fx adjustments (out of 8), so I don't know how difficult it may be to adopt to other cameras.

Twin lens cameras, all. I'll have to see if I can get it to work with my back-to-back Kodak SP360 4K's. Did you notice any tools for synchronizing the front & back cameras?

I did not even know there are 360° systems which use 2 independent cameras. I thought them use 2 lenses but one camera. Wouldn't this mean there should be two separate files in the end?

They are separate cameras---that is, separate synchronized sensors and lenses in a common case. The images may, or may not, be combined side-by-side in a common file. I don't own any of those cameras, so can't say for sure. Some cameras do internal stitching and don't make the original images available at all.

I have been using Kodak SP360 4K's in a back-to-back configuration which yield separate, un-synchronized, files. (Why I asked, above, about synchronization.) Kodak provides a free stitching program that does a good job, but there is a stitching artifact along the seam when I stitch underwater footage. It will be interesting to tinker with the Vegas FX. I've tried stitching it in AVP/Giga, but there isn't enough overlap for good stitching of underwater footage.

Here's an example from a Luna camera. I bought into their crowd funding campaign but they delivered a year or two late & the camera was pretty, but useless. It illustrates a typical file configuration, though (I think).

This video looks strange to me. I cannot even get close to stitch this one correctly in VP16. Maybe another one with some 360° editing experience could help.

Yeah, sorry, there isn't much overlap. I didn't have much success stitching it in AVP/Giga either. I just posted it to illustrate how I think the camera streams are combined in a single file. I can look for a pair of example SP360 files if you want something to tinker with. They have a 235 degree field of view, on land, so are fairly stitch-able.
 

I see. Now I really wonder how it could be possible to synchronize two parts of one frame in one video stream. Time synchronization in digital video world usually means delaying a whole frame or delaying several lines for analog video. This would take two separate files or at least two separate video streams (digital). But delaying only left or right side of a single frame of the same stream? Are you sure this is possible?

I hadn't thought of it that way, but if you crop it into two separate video files (using FFMPEG, for instance) the synchronization error would just be the amount of time for a scan line to reach the center of the image, right? I doubt that would be noticable...by me, at least.

FWIW: my Vuze camera crams the output of 8 cameras, 4 3D pairs, into a file with 2 video streams & seems to be perfectly synchronized.

Here's a google drive link with some SP360 4K footage, if you feel like tinkering---front view, rear view, and the files stitched using the Kodak software. The cameras are not synchronized, so I tap the tray to create a spike on the audio track to help synchronizing them. The cameras hang upside down on my tray, so the images will be upside down.

https://drive.google.com/drive/folders/1ZwebG5j9AbQi-R1lQWvZ5w3xW5-v6N1H?usp=sharing

Thanks for these file. Though I still can't manage them in regard of stitching. Seems like to be rather non-standard.

You're welcome. Guess I'll have to tinker with them when I get V16 next week. (Too busy this week.)