I'm not against they idea entirely. Gene Rodenberry was involved in Star Trek: The Motion Picture but most people will tell you they like Wrath of Khan better. I'm a Whedon fan, but I don't want to be so close minded to say a good Buffy movie could not be made without Whedon.
They should wait another ten years, and then at least get someone who will Joss would give his blessing, to smooth the transition like Abrams recently did with Nimoy. Right now its basically the guys who gave us the original mediocre film wanting to move ahead with no real tangible artistic vision as of yet. Their pitch so far is weak: A new version not featuring the characters that made like the concept in the first place. Not exactly promising.