[KevinH]

It might help if you could provide an example of an output plugin that would need to know you have already done a save or save-as to a file before launching it?

Perhaps a flag that indicates if the current version inside of Sigil passes FlightCrew, or epubcheck or even just an enhanced sanity check might be useful for some conversion style output plugins? Take epub3-itizer as an example, it handles that by simply telling the user in the docs, to make sure the epub2 has passed flightcrew/epubcheck and they have renamed files to .xhtml before launch.