Hmmm I don't think Opeth would be selling out by making a short brutal song...
Being a musician is being a showman, in part...and in a show you need to get the people moving (at least....a heavy metal show...)
So, for the fans, they can make a short violent one (and 6 minutes isn't short by most death metal standarts...but Opeth never cared for standarts
) and not be selling out. Selling out is trying to get more fans (thus more money) by making more appealing music. That infers changes made to music just to get in touch with people that would have nothing to do with the band in the first place. If Opeth wanted to get in touch with all the people that would already be receptive to their music, by touring much/promoting/etc., it's not selling out. If they direct their music in the sole intent of getting more fans, it is selling out.
Since one of Opeth's many sides are (controlled and reflective) brutality and (controlled and reflective
) ballads, it wouldn't be selling out to put songs like these in another album. Not doing so (per example, making a one song CD such as A Pleasant Shade of Grey from Fates Warning) would indeed be a good surprise or evolution, but they don't need to.
I think that accessibility in metal is something really touchy. It can get mixed up with emotionally-charged art. Some accessible brutal death metal (let's say...Six Feet Under) doesn't differ at first earing from researched, artistically fullfulling death metal (Cryptopsy). So a sound change doesn't indicate at all a move towards accessability, at least in my opinion
and since opinions are worth nothing, you all just lost 3 minutes reading this post
.