I have just tested preview of raw files (CR2) in Kstars FITS Viewer while capturing with Ekos.
I have installed dcraw and cjpeg on the client side and still cannot get the preview. Instead I've got a warning msg pop up that a file does not exist - see attached screenshot for details.
Any idea how to get it working?

I'm using Ubuntu 16.04 and Kstars-bleeding 5:15.12+r5690.252~ubuntu16.04.1.

Thanks for your report, issue fixed.

Confirmed. The functionality works as designed.
There's one more question though - as for now each captured file is opened in a separate window of Kstars image viewer. Could we bind it to Kstars FITS viewer instead? This would be really handy to keep all the image outputs in a single window. Example use case being routing the viewer window to a specific display i.e. when streaming observation session to the Internet. If not, could we use single window preview for consistency with Kstars FITS viewer behaviour? OR let a user choose how this files are handled by the viewer in Kstars options?

I updated it so that it keeps one image viewer window but I didn't test it. Let me know if it works.