I'll admit I've been out of the field for a long time... I sort of cut ties and haven't read up on the latest tech in probably 15 years. Your point about missiles receiving mid-course updates is very interesting, though. I have a couple of questions...

Has any (unclassified) work been done on rear-mounted weaponry? I mean, if missiles can have modern CPUs and targeting software, can't the countermeasures have those as well? It seems like accurate, rear-mounted, auto-targeting machine guns (or heck, lasers for all I know) could still be an effective countermeasure, especially if you're in the position of trying to outrun one. That is to say, rather than trying to outmaneuver, outrunning would take you on a straight path, which would put the missile on a more-or-less straight path behind you until it hits. It seems like this is the perfect scenario for auto-targeting defensive cannons.