Relax.
Metallica is only following a trend. Phish has done this for a couple years (
http://www.livephish.com/), as has Pearl Jam, though they each have taken different approaches.
Dave Matthews Band also announced that beginning this summer they will do this as well.
There are pros and cons and it depends on the artist. I know very little about Pearl Jam and Metallica's sound systems and taping community, so I can't comment.
As far as Phish and DMB, its not a big issue. Taping is completely unaffected, and there will be many shows which will sound better from the taper than the copy made for sale.A couple of days of production will not make it sound all that much better than some of the recordings tapers pull at these bands' shows.
As far as DMB, the SBDs won't sound too bad, I assume. They have six microphones placed around the ampitheatre to pick up crowd noise, so I assume that will be on the CD.
However, just being a soundboard does not mean it will sound better. This can be done very very very wrong and end up sounding terrible. If the bands start editing, or recording over misplayed notes, or things like that, it will be sh*t.
But, as for the effect on trading communities, it doesn't matter. Pearl Jam openly encourages trading of their live releases. In the end, for an established trading community, it is be a good thing. We end up matrixing the AUD and SBD and sharing them freely.