I am jailbroken on AppleTV software 5.0.1. And, well, good news: I checked Firecore's Maintenance app this morning, and "Remote HD" is now being offered again.
I see @firecore mentions it on Twitter as well: https://twitter.com/firecore/status/213999259857584128
Once installed, a new button for "Remote HD" appears on the home screen. Click it -- and all that is in there is the version number (4.4) and a menu command to "Hide Menu Item." Bad news, however: if you select that, all it does is hide the version number. The button (now even more useless, as there's nothing displayed when you click it) does not get hidden from the Home Screen. Also, I see no way to "unhide Menu item," either. And rooting around in .plist files isn't getting me anywhere! Ack. Is there any way to get that version # menu item back, and if not, just hide the Remote HD button entirely, as I'd expected?
Lastly, it appears that "uninstalling" RemoteHD via the Maintenance menu doesn't work properly either. I mean, the button disappears from the Home Screen and you can connect via RemoteHD any longer, but Maintenance still lists it as "Installed." I had to fix this, somehow, by installing and removing it again via NitoTV.
So check this great app out, and be happy it's available again... but tread carefully if you value a clean and sensible home screen on your AppleTV.