This contains a number of changes, but they all look clean and straightforward based on reading the code. I tried killing the WeakArray finalization process, then saving and restarting the image, and everything came back fine. It's late in the release cycle, but this change set may prevent serious and hard-to-debug problems for Squeak users. It is relatively low risk, so I recommend including in 3.7 if possible.
Very minor nit (that should not prevent inclusion in 3.7): InputSensor class>>startUp should not be in this change set. It just adds an unneeded carriage return to the source but otherwise does not change anything.