This game (though I suppose it's about 10 years old now) was one of my favourite of the time.  From the way the game ended I always thought there would be some sort of sequel in the works.. it was a little bit of a cliffhanger, but nothing was ever really came out to follow.  It may be quite a time gap to ask about any kind of thoughts towards a sequel or a remake, just curious to know if there ever were plans to make another that just never came through.

A Shadowcaster sequel would be cool, but I honestly don't think it is something Raven is ever going to make (but who kows, right?  Morphing into a Dragon with todays graphics would be awesome).  I felt the urge to play the original again a few weeks ago, but I couldn't make it run on my computer anymore. :(
a more realistic concept would be a port to Gameboy Advance, in my eyes at least.  ...come to think of it, a Black Crypt, Heretic or even Hexen (might be pushing it) GBA port would also be really sweet.  :)  I'd definitely buy one of each (two of H/H, for mp).  I'm actually somewhat surprised that this idea hasn't been jumped on, especially considering the popularity of GBA Doom and Doom2.