Why?

It's been 20 years. The bloom is off the rose with Whedon and he probably wouldn't be asked back. As NuTrek (among other shows) has shown us, revivals like this almost inevitably suck. And a reboot or universe won't have the magic of the show you loved, it'll just be a soulless cash in on a familiar property.

Be happy with the little there was. Treasure it. Because anything new will likely be a horrible mistake that doesn't add anything good, it just tarnishes the original.