Kinda hard to do a Fate/StayNight RP without the servants. Or do you just mean a bunch of mages hanging around the clocktower? If so, "The Case Files of Lord El-Melloi II" RP Might be a better title. Since the Fate/ title usually points towards servants and grail wars. 

You're unlikely to get any interest if your only info so far is "I wanna do an RP based in this world, but not have anything else to talk about since I removed the thing it's most well known for." 

It's like doing a Harry Potter RP, but no wizards or witches or Hogwarts. You gotta replace them with something.

Basically, don't wait for interest before you tell people your idea. Because people don't show interest in Interest checks that only tell you what they aren't about, you dig?