i'm not sure wheter this shall be request for new ebuild or just use flag for impressive package.
there is makebeamerinfo package (https://github.com/jberger/MakeBeamerInfo) accessible through CPAN, which helps to better render outline page in impressive (tab key). if kicks of lot of unimportant slides in overview (e.g. slides which differ in visibility of just bullet or so) which is really helpful in actual presentation.
i would propose new useflag to install this perl script with impressive or new ebuild.
thanks for consideration.