When is it going to happen? Don't say it's a Microsoft issue either. FastPictureViewer can do it just fine for $15. Why can't you? Other apps do it for free! What's stopping you exactly?
Every other app out there can generate thumbnails in Explorer, including 3D apps like Cinema 4D. What's holding Photoshop up for so long? What special draconian measures have Microsoft taken to specifically deny PSD thumbnails from soiling their OS, and no other app?
Acrobat DC does it out of the box now:
Where is that option for Creative Cloud that says: Enable thumbnail previews in Windows Explorer for all CC apps? When is it going to come?
When is Photoshop going to do it? If I sound frustrated, it's because I am. It's been years now of this nonsense. Using Bridge is not an acceptable alternative. I have no use for that bloatware. Don't say submit a feature request either. That's been done multiple times with no result.
There is no excuse any more. Just get it done for heaven's sake!
So use Acrobat DC if you do not want to use other codec packages. Adobe removed that type of support from Photoshop years ago when Adobe started to use Operating system File System Dialog s not Adobe's own dialog s by default. Windows does not display thumbnails for all image file type. I forget what version of Photoshop had that support. You would not want to use it if it could still be installed.
Or just use Bridge when you want to look through psd files