FireCore had released an updated version of their jailbreaking tool – Seas0nPass to support tethered jailbreak for Apple TV software update 5.2.1 for Apple TV 2 few days back.
Apple had released Apple TV software update 5.2.1 last month, which included a number of security related fixes as well as a redesigned Hulu experience.
Apple had released iOS 6.1.3, which fixed the lock screen bug and also killed the evasi0n jailbreak. Apple TV software update 5.2.1 also killed the untethered jailbreak for Apple TV 2 as it also made use of evasi0n.
It seems highly unlikely that FireCore will release an untethered jailbreak for Apple TV 5.2.1 as evad3rs team has already said that they are not working on a jailbreak for a minor update.
Jailbreaking Apple TV 2 enables users to install aTV Flash (black), which adds new features to the second generation Apple TV such as web browsing, Last.FM access, support for HTML5 video sites, stream media from most NAS devices and lots more.