Yeah, we get this kind of post every few years, about porting to whatever shiny new other engine is out there. For reasons already discussed, "porting" isn't even a good term for it, since you'd just be making an entirely new game practically from scratch. Just look at the size of our source code.
The reason we moved to the Doom3 engine it in the first place was only because Thief Deadly Shadows didn't allow us to properly make good FMs. But now we can make FMs and it's open source. If there is some cool tech that the CryEngine or Unreal engines have, it's gonna be about infinitely easier to just port that cool tech into the TDM engine than vice versa, and in fact we've done that for a lot of cool new tech like soft shadows and ambient occlusion and the like.
So that's really the way to go if you want to update the tech. And we're open source so you can do that.
Anyway, all that said, one can still make a cool new TDM-inspired game in CryEngine, and I'd even encourage that to someone up to the challenge. For example I'd love to see a cyberpunk or modern stealth game, and that'd be good project for a new engine.
I just think if they're making an entirely new game already, why not just make an entirely new game.
Well one thing that might be cool is if someone made a game in another engine that could parse a TDM .pk4 file and open up as a map in itself. So then once you've made it, it already as all of our maps ready to play in it. I have an idea that that might not work well though, especially for custom things people put in the map. Also again, we can already play those maps now. If you're going to all that effort, let's have a new cool game with new cool maps!