No, I don't think you can use ISBoxer to round-robin. It seems pretty clear that you cannot use ISBoxer (or Keyclone, HKN, etc) at all - there seem to have been reports of people getting warning from people using ISB with only a single client. At the moment it seems like Blizz is focusing on software detection and reporting - all the known multiboxer tools are getting people warnings.

I disagree with your 2nd statement though - Blizzard has clarified a few times now that they are not banning multiboxing. I don't think we yet know their intent or how tolerant they will be of non-software broadcasting approaches. We know they're fine with people operating multiple toons at the same time on /follow and alt-tabbing between them. (Which almost seems odd because their change won't stop 40-account herb farming - but that's a separate discussion.) But if we come up with a non-software broadcasting method that makes multiboxing almost as effective as it used to be - will Blizzard tolerate that? No one yet knows.

I see a few ways forward that we're exploring now. 1) Hardware multicasting - which I agree may also be problematic from a "spirit of the law" sort of thing - I think I've volunteered to be that guinea pig. 2) Non-multibox software versions of round-robin keyboard input (e.g. using hardware or software system to cycle the input to various clients - think "alt-tab", but faster and keybound to something easier to press rapidly). 3) Non-multibox software versions of controlling window and mouse input such that a user could easily mouse over different windows and provide input to that window easily.