Dan,
I agree that it would be nice to see native support but I feel like so many factors are at play with things like this. I have dealt with spherical images from a few different sources (or cameras) and they are not all the same. There seems to be a 'standard' kind of developing, and it's basically what Facebook will take since they do well with 360 degree photos. If you're outside that standard, then it's a bit of work to modify things to make the images work.
In any case, we have come up with a pretty fast process to throw 300+ images onto a map with spherical support that has streamlined things a lot.
1. Crews take the shots in the field and have each photo geotagged (with us, we have an external GPS unit that plugs in, but with many new cameras, this is just built-in).
2. I quickly throw the photos onto our website server - just a simple drag-and-drop, keeping the native name.
3. I use an open source program called ExifTool (ExifTool by Phil Harvey ) to quickly generate a spreadsheet that spits out all Exif data of the photos, including Lat and Long coordinates.
4. I modify the spreadsheet to add some project data and the linking variable for the Pannellum viewer (it's super quick with just an easy formula from Excel).
5. I throw the lat/long coords on the map (ArcGIS Pro), plot the points, then publish the data. I could stop here but have one more step.
6. In ArcGIS.com, I fiddle around with the popup to make it look nice, show a thumbnail, have a link for the image and that's it!
About 300 photos could take maybe 2 hours to do all this and most of that time is just uploading the photos to the web. (I suppose the step number 1 would take the most time since the crews are in the field, but I deal with steps 2 through 6, haha).
I much more prefer to use my own website for hosting the photos since I can get to them directly and quickly, with the extension intact (the .jpg at the end). ArcGIS.com hosting would eat up my credits for storage.