EVE General Discussion

It's discussed in the CCP Presents video. No physical models yet.

The Megathron will be a 10 inch model produced by Quantum Mechanix
(Based on the Retribution rework of the digital model)

The Nyx will be a 28 inch monster produced by Project Triforce

The Nyx will be made to order, hand-painted, with internal lighting, and a very cool base to stand on.
Count on it being pretty costly as Project Triforce stuff is expensive.
Their larger replicas are usually around $900 each.

As for the scale difference, I don't really understand it, perhaps it's just a cost limiting thing.
Rescaled to 1:4000 the Nyx would be 32.2 inches long, still quite manageable, compared the 28 inch it is now.