Since mod downloads for the Xbox platform would violate the following part of the terms of service, they are not allowed, nor will they ever be on the Minecraft Forums
14. Service Operation and Equipment.
You may only access the Service with an Authorized Device or by logging into your account via the World Wide Web. You agree that: (i) you are using only authorized software and hardware to access the Service; (ii) your software and hardware have not been modified in any unauthorized way (e.g., through unauthorized repairs, unauthorized upgrades, or unauthorized downloads); and (iii) we have the right to send data, applications or other content to any software or hardware that you are using to access the Service for the express purpose of detecting an unauthorized modification. You must not attempt to disassemble, decompile, create derivative works of, reverse engineer, modify, further sublicense, distribute, or use for other purposes the Service, any game, application, or other content available or accessible through the Service, or any hardware associated with the Service or with an Authorized Device. If you do so, we may cancel your account and your ability to access the Service, and pursue other legal remedies. We may take any legal action we deems appropriate against users who violate our systems or network security, this contract or any additional terms incorporated or referenced in this contract. Such users may also incur criminal or civil liability.We reserve complete and sole discretion with respect to the operation of the Service. We may, among other things: (i) restrict or limit access to the Service; (ii) retrieve information from the Authorized Device and any connected peripheral device used to log onto the Service as necessary to operate and protect the security of the Service, and to enforce this contract; and (iii) upgrade, modify, withdraw, suspend, or discontinue any functionality or feature of the Service, any game or other content available or accessible through the Service, or any hardware or software associated with the Service or with an Authorized Device, from time to time without notice. We may do so by the automatic download of related software directly to your Authorized Device, including software that prevents you from accessing the Service, playing pirated games, or using unauthorized hardware peripheral devices.
This has been discussed several times, this thread is now Locked for Redundancy