what is behind the lack of rear-facing defenses/missles, etc.  or not even rear facing but, well...why would we limit our most advanced planes to have to point the nose in the direction of our intended target?

As far as I know, no one has been able so far to solve the aerodynamic problems with launching missiles in a direction significantly off the aircraft's velocity axis.  Missiles launched to the rear are not sufficiently stable enough in the initial portion of their flight to remain in controlled flight.

It's true that most aircraft still have to point in the general direction of the target.  In general this is because of the need for some sensor on the launch aircraft (virtually always the airborne intercept radar) to track the target and pass information to the missile or otherwise enable the missile to track and hit the target.  These sensors have a limited field-of-view, and thus only cover a sector to the front of the launch aircraft (although the F-35 is changing that to some degree).  However, there are advances in High-angle Off-Boresight sighting systems and missiles that do/will allow the engagement envelope to be extended far to the sides and even to the rear.  This includes things like Helmet Mounted Sights, missiles with extremely wide gimbal limits to their seekers to allow a lock on to targets well to the side/above/below the launch aircraft, and missiles with a datalink capability that allows the launch aircraft to launch a missile without first achieving a lock-on to the target, and then to send updates to the missile in flight so it can achieve a Lock On After Launch.

Gee, I'd like to see some detailing of the craft's belly, of the intakes for instance, and where these bays would go.  I'd also like to see a valid treatment of the tail, which this isn't.  And I believe it is expected that Meteor, AIM-120-NEXT, JDRADM will wipe the thick-lipped smirks off some faces at Vympel.

 

OTOH, I do believe that air forces should be looking at countermissile technology.  Unless the US solution is DEW, we certainly should be working on it... at least it would seem to pay off in facing the S-X00 threat; a missile the size of a house should be easily acquired and not too hard to engage - after all you know where it's going! ;>

1. Part of the reason is that you can dodge more easily turning into the pirsuit than by trying to rin from it. If you just run, then it just corrects lead and run s you down, if it has the energy.  If it doesn't then why worry about a dodge or shoot at it>

 

2. Another part of the reason, is that missile versus missile in a four body problem is tough enough in head on pass or stern chase. Suppose you want to shoot at a chase missile while you run from it? Not efficient: its easier and more successful to run the chase missile out of potential energy or to use countermeasures either physical or electronic to decoy it away.

 

3. You also have load to consider. How much mass do you give over to a defensive missile system? The more you point weaponry backwards at an enemy, the less you have for OFFENSE. The whole purpose of a fighter is OFFENSE.   

 

4. The launch of a missile into a jet plume, others mentioned. If you use IR defensive missiles which the Russians tried, it doesn't work to well as the seekers fry. Even the radar homers didn't like the heat wash, not to mention that the missiles fell out of control from the plume's turbulence.

 

 

. 

The Wiki article that I used as a reference has some pics of the technology demonstrators, and some shots of a mostly-completed prototype.  Granted, it's Wikipedia, but the article had some solid links, so it may not have fallen to fanboyitis.