@paulfiera - no, obviously not yet.
Thousands of lines of code related to Modify ePub has soaked up most of the last few weeks, and there have also been multiple releases of Count Pages, Generate Cover, & Reading List. Then add to that Extract ISBN got broken with calibre 0.8.53... oh yeah, I do have a day job too...
@JSWolf - correct, there is no option for general broken link checking. With recent releases of this plugin I have started tumbling down the slippery slope of all sorts of potential internal ePub content validation. My initial additions to this plugin were focused around things that calibre had responsibility for breaking (until recent fixes), like broken image links and broken NCX links. Having opened the door a crack with those, it is not unreasonable to consider other things eventually. Of course it is pretty much replicating some of FlightCrew validation, the difference being that this plugin would allow you the 50,000 foot view of which books have issues across your library, that you can then open in isolation to fix.
As for the TOC/NCX naming, that was deliberate on my part for historical consistency but it is a fair point. The issue is that the very first option I had for QC was "Check TOC with < 3 entries". That was named that way so as to not bamboozle users with the term NCX, as I would suggest only a very small subset of users would understand what an NCX is. However you are 100% technically correct that all three of those options should state NCX. Perhaps a good compromise is "Check NCX TOC with < 3 entries", and then if we ever have checks related to an inline TOC we say "Check inline TOC ..."
Oh look, 3000 posts...