Well, I think the issue here isn't whether or not they should use some of their energy working on and recording covers, but rather their MO while in the studio. We have no clues on how are they going to use their studio time for this album, but usually what they do is gather together in the studio, write an album worth of music, record it and that's it, they leave. The album then goes to the "production" phase where it gets mixed, mastered, etc, so the rest of the guys just shift gears and get in touring mode or promotional mode, whatever.
In other words, they get in the studio, do their thing, and then leave. They usually don't get back in "studio mode" until the next album cycle, and that's been their MO for most of their career. It'd be silly to expect otherwise, I think. So, in that context, spending some of their limited time arranging covers and whatnot could be considered a total waste of time. On top of that, we don't know if their deadline is just before Mike and Jordan go away to do CTTE or if they'll get back together after to keep writing/recording. If it's the former, then it leaves them even less time to do that.
Now, in my personal opinion, I just don't understand people actively wanting the band to cover other people's songs. Just listen to the originals, guys. The world definitely needs more versions of the same classic songs from the same classic bands. But, again, that's just my personal view.
I agree with Scotty's take on original material, though. Why settle for the first 70-ish minutes of music you came up with when you can keep writing and trying to get even better stuff and then choose the best songs from the bunch? BUT, that's just not how they work anymore, and they haven't since the 90's.