the ebuilds for the 2.x.x versions of media-lib/openjpeg should create symlinks in /usr/include/ for the *.h files in /usr/include/openjpeg-2.1/ similar to the ebuild for version 1.5.x. Otherwise some programs depending on openjpeg have probems finding the include files. Reproducible: Always
Since openjpeg 1.x and 2.x can be installed alongside each other, this would probably also need an eselect module, I think.
I'm not directly involved with this package but I think that the programs using openjpeg should be fixed, especially if they are being built with Portage otherwise the build will fail depending on what the user has selected. Maybe you were referring to software being manually built by the user?
I am not aware of any packages failing to build against openjpeg-2 at this point, and none have been cited. Thus I am closing this bug as invalid.