The problem with doing this automatically is that there is no good place to put it. The logical place to put such a feature is in DCR. However, DCR doesn't actually communicate with the device (not yet anyway), so it wouldn't know if the device is unreachable or not. If you put the feature in RME, then what if RME isn't available?
That said, there are some features to aid with trimming devices. Campus Manager has a script called DeleteDevices (under NMSROOT/campus/bin) which allows you to delete unreachable devices from Campus Manager only. In Common Services 3.1 (part of LMS 3.0) when you choose to delete devices, you get a pop-up asking if you want to delete all the devices, or just those that are not managed by any application. While this still wouldn't give you what you want, it may help prune other unwanted devices.
