Mojang have now opened up an interface for mod developers to propose changes or inclusions to the future Minecraft API.
Using this issue tracker, you can submit a formal proposal for the Minecraft API for vetting and to stimulate discussion around your idea. ... While we are in the beginning stages of building and designing the API, a lot of the requirements will be relaxed: for example, a MAPR will not be required and the vetting period need not apply. At the start we want to foster discussion of ideas and needs, rather than being completely formal about submitting a proposal for a new addition to the API.
This uses the JIRA system, like the bug reporting system for Minercaft Pocket Edition (cf. Where to report Minecraft Pocket Edition bugs
So if you are a closet java modder (or may be a mod developer who makes closets), say your bit and let Mojang know what you think are vital things to include in the API.