I've been longing for a Windows EPUB IFilter DLL for a while, I think I've found one. Actually it has been on my radar screen since November last year, I just never got around to installing it, and trying it - sort of forgot about it.
It's a modified version of the Sumatra PDF IFilter, see ==>>
xplorer˛ blog: search filter for EPUB ebooks
Search seems to work well, I did some tests on 30,000+ epubs in Windows File Explorer, search times were sub 5 seconds, which is the same as searching the companion 30,000+ DOCX files. As expected I had to rebuild the indexes after installing the DLL.
I could only get the Plain Text Preview feature working in an old payware version of xplorer˛, maybe there's some way to get it working in File Explorer I'll ask the xplorer˛ developer.
Not sure if it would It should work in xplorer˛ Lite which is free.
If I find anything new, I'll add a post here.
BR