One of the things I thought, and I suppose was slightly concerned about, after Alter Bridge fell into the routine of regular Slash /Tremonti with an AB album every 3 years, was that it might limit the amount of growth and experimentation (for lack of a better word) in Alter Bridge music. I know that experimenting is a risk (after all there's every chance they might change to do something I like less rather than like more) and I am not hoping for them to drastically transform their sound; I want them to stay Alter Bridge... But if they stuck with Alter Bridge more consistently (perhaps more touring, a bit less time between albums, all other activities confined very much to "side project" status) then they would be very comfortable with "being Alter Bridge" already, and perhaps be able to say "Last album we were Alter Bridge doing this, how about we try being Alter Bridge doing that instead?"
However, with going away from Alter Bridge for such long periods then coming back to it, just "being Alter Bridge" again becomes a bit of a novelty in itself. Mark and Myles put a couple of pieces together, the band bang out a classic Alter Bridge sounding tune, and think "we're back baby!" (As you can tell I have been a fly on the wall during their latest studio sessions). And they probably know that we as fans will be happy to hear that familiar AB sound again too. Maybe they come up with a couple of more outside-the-box songs too, but it's their first time writing any Alter Bridge material in a while so just doing something in the vein of AB feels fresh enough after doing Slash, Tremonti, etc. for the past 2 years.
Basically, having to recapture the Alter Bridge sound each album (and perhaps also feel like they have to deliver a quintessential AB experience to the fans each album) might leave them a bit complacent to stick with what's familiar. This even extends to things other than making the album, like touring. Coming back to playing Alter Bridge again after a couple of years, they're going to want to brush up on the classics and touring staples before thinking about rehearsing an old less played song. And when they come back to a city they haven't visited in 4 years and are unlikely to again for a while, they're more likely to think "Hey, you guys must be ready to hear Before Tomorrow Comes Again, right!?" than to change up the set list from last time.
A bit of a ramble, and to be honest I realise that it hasn't really turned out that way so far. Fortress was a great album, and songs like Cry Of Achilles and Calm The Fire were both different to AB's previous work and among their best songs. Plus, I am not saying "experimenting" is necessarily better - for all I know, keeping AB feeling fresh to the guys with regular breaks might be all that's preventing them from "experimenting" by adding some dubstep or reggae into the mix. But seeing the talk about experimenting and what sound to hope for on the next album, it reminded me of these thoughts from last time AB were releasing an album, that are still valid now.
Personally I hope that the album is quite similar to Fortress - not necessarily in its sound (although that wouldn't be too bad, as Fortress is great and like I said, I will be happy to hear any Alter Bridge even if it sounds very familiar), but in how it surprised me with the feeling of actually being an improvrment and containing some stuff that really did sound like Alter Bridge "experimenting" to positive effect.