I had a thought today (few and far between, i know).  In 30 years, ALL transferable machine guns will be C&R's.  That thought made me smile a bit, although I will be an old man then (63).

I think the ATF is going to be on top of it.  

There is already lots of machine guns that are C&R now. They are still under NFA also. But all it means is you get your tax stamp, then have it shipped to your door

Check the books the ATF sent you. They're listed in there.

I think all of them should be C&R right now. With only ~300K on the books as transferrable to individuals, they definately derive their value from being novel and rare. Look at the number of "limited production" pieces on the list where limited means a couple thousand. That pretty much describes every model of machine gun. How many registered FNCs are out there? Uzis? MACs? M16s? Treating each model seperately, as they should be, they all can be said to be "limited production".