I had a discussion with one of my friend who's also a huge Opeth fan and both of us agreed about the fact that Opeth should do a huge concept album. What I mean by concept album is full lenght story spread on two cd's. No dark/light side thing. Everything mix, long songs, short interlude, experimental break, etc. Lots of band made legendary records of that kind. Just think of Pink Floyd - The Wall, The Who - Quadrophenia, Genesis - The Lamb Lies Down on Broadway, etc. I think Opeth reach a level of musicianship that could do that kind of stuff.