Recently heard at my Colt Armor's course that HK is working on a G36 upper reciever that is supposed to be a drop in unit on a AR15 M16 lower reciever. Sounds interesting.
PAT

I heard it looks like an M4 upper, but has the G36 gas system.

The current PMOD from CRANE is looking for replacement uppers with an "improved gas system". I have also heard that H&K is working on a G36 based upper replacement, this could be a home run?

As for the optics mounting, I doubt that would be a problem, the PMOD states that the new receiver must be capable of mounting all current SOPMOD goodies and no modifications can be made to the lower receiver.

Interesting to see what comes of it...

hmmm... I'm intrigued!

GIMMEE!

Are they trying to fix a non exstent problem?  What is wrong with the current gas system that needs replacing?  A rifle doesnt stay with the military over 30 years for being a POS.  Im just curious at what these "think tanks" are forseeing.

Will it look like a G36 upper?
How much will it cost?
When will it be available for sale?

As much as I like the AR15 it does have a few major problems. Most deal with reliability in harsh climates. A G36 is as reliable as an AK. That would be a nice mix. All the AR's ergonomics with the G36's reliability.
PAT

The AR's direct gas system blows a lot of crud into the action of the weapon, hindering reliablity and fouling the weapon faster than it ordinarily would.

Delayed gas systems work better all around. Even Stoner knew this and incorporated this system in later weapons he designed...

Rhino did this 20 years ago or so.  It's pretty simple really.  Replace/modify the front sight housing for a gas valve/chamber.  The little gas tube is replaced with a larger tube incorporating a piston and return spring.  The hole in the upper for the gas tube is expanded to allow the rod to pass through.  Replace the carrier key with a slightly different one for the piston.  Get rid of the 3 rings on the bolt.  You're done.  On the Rhino system, there were three settings on the gas port so you could increase the amount of the gas for fouling.  When you don't exhaust the gases into the receiver, it stays cleaner and cooler.

I doubt we would go to a polymer upper.  While you could do it safety wise, i.e., add some steel tracks for the bolt carrier to ride on, I don't think it would be stiff enough to maintain accuracy with optics.  For the newbys unfamiliar with the system, unlike a FAL or M14 where the bolt locks to the receiver, the AR bolt locks to an barrel extension.  The receiver holds things together, but doesn't have to contain the stresses of firing.  That's why you can get away with aluminum or even polymer.