Very. The reports of a Sliders feature (yes...feature) in the earliest stages of work are coming directly from co-creator Robert K. Weiss (who is currently working on the idea). Keep in mind, though, that this subject is currently ongoing and not history.
But you ask youself...Sliders as feature film? It's alot more probable than you may think. Robert K. Weiss has a history in Hollywood of taking misunderstood or under-rated television ideas into the realm of successful motion pictures. The first example deals with his Saturday Night Live creation "The Blues Brothers". Not only did this become a motion picture that is now a cult classic, but the original picture even spurned a sequel just a few years ago in "Blues Brothers 2000". An even better example has to do with Robert K. Weiss' short lived television creation "Police Squad". This series did not even make it past one season...and quickly faded into obscurity after it's cancellation. But years later, Robert K. Weiss took the idea of "Police Squad" and made it into a motion picture...a very successful motion picture named "The Naked Gun". And as you well know, this series went on for two more theatrical releases.
So, Weiss has a history of pulling things such as this off...and he has the recognition in Hollywood to get people to listen.
In any case, Sci-Fi has stated that currently they are not interesting in producing a movie...but they also refuse to sell the license because they "still hold value in Sliders". Basically, Sci-Fi doesn't want to sell the license before they see how their upcoming new shows do (Invisible Man, Spielberg Mini, etc.). If those don't do well, then they may want to produce a Sliders television movie to pull in ratings. Ultimately, Sci-Fi's stake in this is limited as they only have the license through 2002, and then it will be up for grabs to the highest bidder. Keep in mind also that Sci-Fi can sell off the license before it expires if they choose.