Apparently, the only "venue" that jailbreaking makes available that seems to be of notable value at this point is XBMC, for those who want to stream AVI files to their TVs without taking the time to convert.
Myself, I use both my ATVs as they are, as all my media is already in iTunes, and I have no problem leaving my iTunes running on my iMac in sleep mode. My AirPort Extreme wakes it when an ATV needs a file, then allows it to go back to sleep.
If jailbreaking allowed me to stream movies directly from my Time Capsule without having to use my laptop's iTunes list first then I'd be all over it. Unless I completely missed something that function is still unavailable and jailbreaking would do nothing for me.
You would need to set up a media folder on the Time Capsule, make it an SMB (Samba) share inside Airport Utility, and add that to your "shared folder" list. That could possibly work, although I haven't tried it. Your Mileage May Vary.
A word of warning: Don't try to access your Time Machine backups directly with this. Doing so has a very high risk of corrupting your backups. Set up a separate folder on the drive's root instead, or create a separate partition on the Time Capsule.