Developers don't like having a lot of different versions of their software out in the world because it means they have to maintain those versions. Adding some sort of default rollback ability implies that devs will have to continue to support those old versions. That's not going to be very popular.
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This only tracks the amount a device is used, not who is using it. If you want to prevent (or at least discourage) unclaimed use, you'd have to tie this to some sort of alert system. You'd probably have to write software that notices increased power draw, checks for a sign-up, and alerts someone if no one is signed up to use the device.
This could work; however, it would only serve to notice violations after the fact. With real-time monitoring, it could catch violations in progress, but someone would have to go, check the device, and yell at the offending party (which mightn't be reasonable). This system probably wouldn't prevent unclaimed use before it happens.
Hm. If you don't want to restrict access to the room, and don't want to restrict access to power, you'll have to restrict access to the machines themselves. You could apply a padlock to a moving part of the device (or perhaps a cage around its controls). You'd then store the keys in a central place and require people to sign out those keys when they want to use the device.
If you don't want to rely on people's good faith in signing things out, you could have someone else control the keys. This would require some manual work, but it could probably be done by a department secretary or someone else who's already at a desk - you wouldn't have to put someone in the room itself, and it would presumably be a very small part of their job.
You could conceivably store the keys in some sort of container with electronic access control as well, but that may be more trouble than it's worth.
When you chat with Google via XMPP, are you logged in with a Google account or using federation somehow?