I'm never a big fan of reboots or recasting, and Kolchak would be especially hard to recast. Johnny Depp really isn't the type. I don't think he can pull off the rumpled, rough-around-the-edges, worse-for-wear type. I'd have to think if there are any contemporary actors who could do it. Darren McGavin is a tough act to follow-- pretty close to impossible, in my opinion.
And how exactly will they handle this? Will it be a remake of the original movie? Will it be set in 1972? Or will it be a new adventure for Kolchak, following the show in 1975? Or will it be set in the present day? As with all remakes, the ways to screw it up are nearly infinite, and the ways to get it right hard to imagine.