Thanks for the link. From my quick look at it there isn't much overlap of the two functions. That tool you linked to looks like something that should or will be functionality in Sigil, as the majority of it that I saw listed involves interactive editing of the ePub.
There was only one automated function I saw that would be applicable in theory and that was zeroing margins. However even that I think is too crude a thing to be doing and instead needs to be done manually IMHO. Otherwise you will lose any appropriately margined subparagraphs. It is using a sledgehammer to crack a nut and expecting to get anything edible afterwards
. If you looked at the book first to know that it was safe to do so then the function could be used, but again that sounds like it should be part of Sigil.
This plugin is about applying changes in bulk in a non interactive fashion, other than choosing your set of changes on a screen before it begins, a bit like converting files in a sense. So there are certain things that quality check can detect in bulk that it then makes sense to fix in bulk. So far it does things like removing legacy or all jackets, zeroes xpgt margins, remove missing manifest entries, remove/add unmanifested files, remove iTunes files and remove calibre bookmarks. All of these have a matching search equivalent in Quality Check.
Longer term I would think this plugin could have features to add/update the cover image, update the book metadata, add/update a jacket etc. The plumbing is there. The biggest issue to not doing these now is that the calibre code to do these features is all based around assuming an oeb object. I instead chose to load the book into the more lightweight container object, to be guaranteed that the disruption to the ePub content was minimal. So I either need to replicate the calibre code, or find a way to combine the approaches, such as also generating an oeb object to call calibre functions, and then copying the bits it has generated into my container.
Perhaps Kovid or someone who knows the conversion pipeline may have some thoughts or suggestions on this.