I think the best solution after thinking about it would be to key the RJ-45 connector if it posed a threat to other hardware.
I agree with this- so far, keying connections has been the best way to try to prevent issues with people plugging the wrong connector into the wrong plug. If it only fits one way and only the right connector can go in, there's not a lot that can go wrong. And for most connectors like this "forcing" the connector will damage one or both. (and seriously, when somebody is actually considering using a hammer to plug in a connector, it should be about time they re-analyzed their approach).
Another method might be, not to key the connectors, but maybe use a different connector- not in form- but more in where the wires go. For example, instead of a "traditional" connector, they could have the leads which supply power, say, on the side. that way if they are plugged into a "traditional" ethernet connector, the "power" is not connected to anything. Those devices equipped to support it will of course have the leads for those pins and accept their input.
In a lot of ways, Ethernet connections have already replaced the use of Coax and other video sources in a lot of applications... I know a lot of restaurants/stores with big screen TVs constantly advertising get their input from Ethernet (of course, they are not powered through the connection), so it's already quite do-able.
