@charles - I'm going to need to think about what you said but fundamentally it sounds like what has been niggling in the back of my mind - wanting an author-centric view of the duplicates for this mode.
I think from as per my last few posts that it also requires different logic in determining the groups contents, rationalising/managing them as you navigate and any applying of exemptions.
Using the tag browser to give the author centric filtered view is a great idea, particularly as you say you can quickly rename authors or ctrl+click to see certain combinations of authors you want to focus on.
The "one group at a time" using restriction instead of search is something I hadn't considered. I guess my only slightest of hesitation is that our reliance on restrictions will preclude the user from (easily) doing any kind of more generic searching while they are contemplating that group. Say for instance you wanted to for some reason see all the books for that author. You would have to exit duplicate search mode first and then start it again.
However that "limitation" would also apply to the show all duplicate groups mode which has a restriction. And perhaps it really just isn't necessary, you have the books you are considering duplicates in front of you so what more do you want
I'll apply the restriction for one group at a time - at least that way the behaviour is consistent with show all groups.