MTH never did one in Railking...if they did, I would've bought one!!
MTH has definitely done the Duplex multiple times as a Premier line, product.
Lionel, however, has offered a Lionmaster (think Railking) Duplex in TMCC and/or Legacy in the past. It is an 0-31 curve capable engine. I am leery to preorder Lionel based on quality issues but will undoubtedly preorder again if they bring it back. Given the reappearance of Lionmaster products with LC+/LC2, I'm hopeful we'll see it again sooner rather than later. And yes, I'll certainly preorder one.