Good to hear. I didn't know that LostWinds uses the same engine.
Lostwinds & its sequel were originally released on WiiWare using the previous generation engine. For the iOS port the game moved to the new engine which could be ported more easily.
I wouldn't be surprised if Metal came to OS X, but that would require Apple to get the GPU manufacturers on board. And even then, I doubt it will completely replace OpenGL.
I think with Apple's current sales figures the GPU vendors will want to stay onside, whatever Apple's plans are. There'll be far more revenue & profit in supplying mobility GPUs to Apple & co. than aftermarket enthusiast cards.
However Apple always plays these things close to their chest & so we'll only find out when they are ready.