And as a sort of "music history", the Allman's ALWAYS had two drummers (Jaimoe Johanson and Butch Trucks; Butch's nephew Derek later joined the band as second guitar player), and in fact, since 1991, have had two drummers AND a percussionist (Mark Quinones). (I think there was a short spell in the early 80's where Jaimoe moved on, but there was a second drummer brought in, I can't remember his name).
The Grateful Dead had two drummers - Bill Kreutzman and Mickey Hart - from 1967 through the present, live and in studio, (with a short period from 1971 through fall of 1974 when Mickey Hart took leave and was not replaced).
Also, Widespread Panic uses a sort of two drummer setup (main drummer, and a percussionist), and Genesis famously toured with two drummers from 1976 (when Phil assumed lead vocals as well as studio drumming) through the present. The Doobies, King Crimson, and Slipknot have all used two drummers at various points in their careers.
I love the sound of two drummers. If the players don't step on each others toes, it makes it so full and rhythmic. Having said that, while I have no doubt that the Mike's could do it, I don't think the material lends itself to that. It might be more of a novelty than anything else. Having said that, I would pay hard earned money for Portnoy to do an album with a second drummer. His arranging skills would make that kick ass, I feel.