It's nice to see the industry warming up to the Retro stuff. We made an XM moderator clone in a functional linear comp about a year and a half ago. At SHOT this spring we saw TROY brought out GAU 15 clones, and at NRA Colt is talking about bringing back an XM177 clone. Their booth gun had a Late Vietnam serial number (maybe they will re-issue or continue the original serial range).
I hope all the hard to find parts see production on the original tooling (handguards, uppers, lowers, stocks, pivot pins, barrels, etc). Retro XM's are a ton of fun - they bring people back to the roots of the platform and are some of the handier, lighter carbines around.
It would be cool if Colt does move forward with that, if Brownells could stock the retro Colt parts for XM builders.