Unlike the Singer project, which was said to be a straight-up remake, this film, based off a treatment by Warren Ellis, has a much different take on the material. Here's an excerpt from the site.
While Singer's version is closer to a remake of the Boorman film, Ritchie's possible take is more in the tone of Star Wars, and, as Ellis noted last year, his version "differs from the prior 751 King Arthur movies in many ways, but perhaps most obviously in that it is very specifically about the gathering of the Knights."
Even though both projects are set up at Warner Bros., the site speculated that the Ritchie project has the edge, since Singer's project doesn't even have a writer attached and Ellis' treatment is complete. Singer also has many more high-profile projects to tend to as well, such as X-Men: First Class, a Battlestar Galactica film and Jack the Giant Killer in development.
Excalibur was released April 10th, 1981 and stars Nigel Terry, Helen Mirren, Nicholas Clay, Cherie Lunghi, Paul Geoffrey, Nicol Williamson, Robert Addie, Gabriel Byrne. The film is directed by John Boorman.