To enable control of the target block/co-ords of the items that use a targeting mechanic.
Specifically I'm thinking of the Compass and EnderEye's Which are locked to spawn and "nearest stronghold" by default.
Justification and Use Case:
Many maps will not have strongholds so it would allow mods to specify an alternate use for the ender eye. Many mods already exist to change compass behaviour, they should continue to be allows to do so under the official API.
Should allow for setting co-ords on use so that plugins where needed can calulate the target on demand.