Sounds like he's going for the Sixth Doctor Take II. Well it worked out so well last time...
The Sixth Doctor was initially erratic and volatile as a result of an unstable regeneration. Moffat's description, however, sounds more like a resurrection of the Doctor as the Oncoming Storm, or at least someone who isn't going to take any crap from an oversized pepper pot.
Hmm, well, I can buy that Capaldi can do "fiercer," but when I watched the TV special that introduced him, I thought he'd be good as a more kindly, Troughtonesque Doctor. I guess not, though.
I dunno--I think each of the Doctors are multi-dimensional and not just one particular attitude all the time. I think it's still possible for the 12th Doctor to be kind and even comical at times, yet also someone who doesn't suffer fools gladly.