[compurandom]

I claim that if the epub has a cover image but not a (marked) cover page, and the extended driver doesn't generate a wrapper cover page during translation, it is a bug, as this is a clear difference between epubs and kepubs that it should fix.

Everything else I agree with you, it's a feature request.

Some preliminary results from my checks...
I used quality check to search for books without a replacable cover.

It found 500 books as follows:
399 either are marked as or are likely to contain only a single xhtml file (will check these later)
101 were left that needed checking

A lot had unmarked covers and after marking the covers, quality check now says they have replacable covers. So, to answer davidfor's question directly: Yes, I found one piece of software at least that uses the cover page: quality check.

I've found two books (I think) so far that even after marking their cover page, quality check says it isn't removable. Perhaps worthy of investigation later, but it's a small number so far so perhaps not.

Some of the epubs with unmarked cover pages were probably originally single html files that calibre split when converting to an epub, and (coincidentally?) split the cover page as a separate file.

Still chewing through the rest...