It's completely irrelevant to whether they are national stories or not. It was a basic, fundamental question tied to why are we still at a point where all cops don't have them. You've answered it (the only one so far). I agree with you that it won't solve everything, but as you say, it will at least get video evidence out there.
Slowly but surely we are starting to see the barest hints of a willingness to prosecute and even convict officers in police shootings. What is preventing it I think is that your average person/grand jury member operates under an extreme deference standard and that most of these encounters are not happening with clear video evidence, it's just one word v another.
As we get more of these, and as more of these are broadcast, one would think folks would be less prone to overdo it on the deference angle and simply apply reasonable, common sense to these incidents and some of these ridiculous shootings will stop or at least the shooters will be brought to justice.
Castile does not appear to have a criminal record, and was a licensed carrier. So all the gun rights folks should be fervently on his side yes?