Well their stuff isn't too technical as far as heavy goes, so it might be a little boring, but knowing Mikael, he would improvise somehow and make it the greatest metal song ever. I hope they never do one though because that would be losing the essence of Opeth... even the heavy flows with the acoustic, the ballads then those blues licks... if you only have one of the above, you get very monotonous as far as Opeth is concerned.