Currently, if a user needs multiple IME frontends, like, for example, Ibus and Scim, they need to search for the the corresponding back end engine for that front end and manually emerge it.

Instead, there should be a special variable like IME_BACKENDS that would correspond to the appropriate USE flags on the frontend ebuild, so that the desired back end engines would be automatically pull in as dependencies.

Say, for example, the user chose IME_BACKENDS="anthy", and then emerge app-i18n/ibus (the frontend), they should be able to automatically get app-i18n/ibus-anthy (the selected backend) without having to manually emerge it.