As you have already know that iOS 6.1.3 firmware launched in March 2013, today Apple also launched an upgrade for the Apple TV providing it to version 5.2.1. Similar to the iOS 6.1.3 firmware upgrade, Apple TV version 5.2.1 firmware also patched the Evasi0n manipulate used to Jailbreak The Apple TV Untethered, and included support for the latest Hulu Plus app too.
Those people who use Hulu much, they will absolutely wish to take benefits of the new Hulu Plus application, but those people who depend on a Jailbreak they would have been stuck on the Apple TV version 5.2 firmware as there was no Jailbreaking remedy (even tethered) for the 5.2.1 firmware.
Fortunately the FireCore Dev-Team have declared over Tweets today that Seas0nPass has been modified to support Jailbreaking the second generation Apple TV on version 5.2.1 tethered. This implies if you do not think to compromise your Untethered Apple TV Jailbreak you can upgrade to version 5.2.1 firmware and then re-Jailbreak using the newest Seas0nPass.
Remember that, it could be a while before another Untethered Apple TV Jailbreak is launched so we suggest only improving to 5.2.1 if you definitely must get your arms on the new Hulu Plus application.
You can get the new edition of Seas0nPass from here.