This requested feature seems like a strange solution to a "problem" that has been asked about many times.
I personally don't find the current behavior to be problematic. Because I access my files mostly through MC and when I am in the file system, I can easily ignore the .jpg and .xml files. Or use a wild card to find what I want. But that's me. I understand that others find this behavior of storing the sidecar next to the main file to be "messy". It is. It's just a mess I can ignore.
So asking for *one* of the files to be hidden makes zero sense to me. If the behavior is going to be fixed, let's fix it correctly. If JRiver is going to spend time on this, why not make an optional setting that stores sidecar files in their own directory? For that matter, the JPG files could be in that same directory. This would clean everything up and make people here happy.
On the other hand, it also introduces two new problems. First, the sidecar files could now have overlapping names. Second, the main point of the sidecars is so they can be imported into a fresh copy of MC, should the database be lost. How would you now tell MC to go find all of the sidecars for the video files you are importing? A global setting for the sidecar location I suppose. Assuming that you don't lose your sidecar directory when you lose your copy of MC (presumably due to a drive failure or other disaster).
So now that I've talked myself in a circle, I'm not sure there are any good solutions other than turning off sidecar files. A feature that already exists.
For those of you who are asking for the "hide xml file" feature, would you like it better if the sidecars were in their own dedicated directory? Or no.
A deceptively difficult issue to solve...
Brian.