The rest of the packages in the portage tree that have optional support for libidn2 require both use flags to be enabled in order to use it. bind and bind-tools are the only packages that have a conflict between the 2 use flags. Since it makes a lot more sense to use the idn useflag to enable support for idn and the libidn2 useflag to switch between implementations like the rest of the packages do, I think this conflict should be removed.