New version of HoneyView, starting with 5.23, now includes a preview handle for WebP files as well as PSD! And thus you can now preview them in Directory Opus!
http://www.bandisoft.com/honeyview/
HoneyView is one of my top favorite image viewers and now it's even better! I personally use it a lot to read mangas in CBZ/CBR format (supports image viewing from most archive formats).