I think at this point it is very obvious these were the Russian separatists (i.e. disguised Russian military) that brought this airline down through a misidentification. So what does this mean? Should we have tried to interfere in Crimea? I say no on that. This is a step up from that though. If it was Russian military hardware, Russia is about to face some huge sanctions. I still don't see military intervention as a possibility as going into Ukraine is a totally different thing than going into Iraq.
The reaction of the market yesterday and today shows that most consider it a short term crisis (along the lines of the US bringing that airliner down over Iran many years ago).