A hex on you Idolse
From a user perspective I think putting those sorts of checks in Quality Check is fine. The gate got opened when the "check EPUB for jacket" was asked for. May as well jam it open now
As for adding those features - well to be honest I wouldn't quite know where to start in terms of what I should be "looking for" etc for most of them. If you want to see them happen I would suggest one of two things. Either write all the changes yourself using the latest version of the plugin, send it to me and I will review it and release it. Or alternatively PM me some code snippets/pseudocode for what needs to be done for each and I will take a look at it after I clear some other things out of the way like the duplicate finder plugin.