In my line of work (security research), WebSockets are becoming increasingly common as a way to mask malicious activity. Fiddler does allow you to view a WebSocket and display the blobs exchanged. However, I have ran into some issues when the data is compressed and there doesn't seem to be native support for decompression. A workaround was suggested here: https://fiddler.ideas.aha.io/ideas/FID-I-103
More generally, it would be a great feature to be able to replay a WebSocket in 'offline mode', similarly to how you can replay HTTP/S Sessions via AutoResponder.