Source: PlanetHalfLife
Related: Black Widow Games

PlanetHalfLife got some more information from Neil Manke of Black Widow Games about the question whether or not They Hunger will be remade for the Source Engine:

"Developing a version of They Hunger for HL2 would require a LOT more work than the original implementation for HL1. HL2 technology requires a much higher level of detail for each map, monster, scenario, artwork ... literally everything! An obviously, we are not even considering the alternative of providing a quick-and-dirty direct port of TH to the HL2 engine (without taking full advantage of the new technology) because we feel an inferior version wouldn't be fair to our fans. So, since HL2's release, we've been trying to find a way to implement this project and, in particular, we contacted Valve to see if they were interested in supporting us somehow (since TH was the most popular SP mod for HL1), and we are currently waiting for their feedback. In the meantime, the idea of a TH project for HL2 is on hold. That's the whole story to date!"

Check out PlanetHalfLife and Black Widow Games for more information. We will keep you up to date on this.