I'd really like it if there were an option in the downloader's file import options to exclude previously viewed files from the import.

The reason I'd like this feature is that often I'll run a query, get a bunch of pictures, get partway through and decide the query isn't high quality enough to be worth viewing and delete all the remaining pictures from the query without even looking at them. But I haven't really rejected those pictures and would still like them to show up in future queries.

On the other hand any picture that I have actually viewed in the system's media viewer I have made a judgement about as to whether I want to keep it or not. So a picture having been viewed but not currently being in hydrus is a perfectly reliable indication that I don't want the picture and that it shouldn't be imported.