They Hunger: Source Demo (outdated) file

Nope. It's not even a remake, it's a port.
It doesn't have same objectives as "They Hunger: Again", which is in fact a first remake ever made.
Our objective is to port ORIGINAL They Hunger assets to the Source engine, frankly.

Oh ok, fair enough, I think, what does the player actually gain then
over the brilliant original?

Enhanced lighting, ragdolls, high resolution textures, and etc etc. Briefly - everything that source engine can do.

Will there be source code release?

have you installed right version of Source SDK Base 2013 Singleplayer?
have you installed Half-Life: Source?
have you restarted steam after putting the folder into the "sourcemods"?

yep, all that is in place..

then idk, mod works for us, i checked

I don't know either, but any other source mod works fine...a mystery..

This particular modification has no problems, it seems that the trouble is on your client-side.

you're probably right, but what I can do is over my head, I'm not a modder or mapper, I just play stuff. I wonder if anyone else has this problem..

Yes to all and it does not show up for me either.

From what i know, sourcemods are supposed to be installed on Disk C:
If you have it on other disk, try again, but moving it on Disk C:
(example - C:\Program Files (x86)/steam/steamapps/sourcemods)
Also try flushing your steam config - Win + R and type this command:
steam: // flushconfig (without spaces)
After that restart your PC and check if mod is in library.