You may recall BenzBoost reported that the new motor would be a 4.0 liter V8 last year and in one of those reports stated the M177 would have more in common with the M270/M274 four cylinder engine family than it would with the M157 V8 currently used in the new 63 AMG models. The M133 in the new 45 AMG's is based on that four-cylinder engine family.
One should not expect double the output of say a CLA45 AMG as that would put the C63 at 710 horsepower. One should expect the C63 to hit 710 horsepower with tuning relatively easily though unless Mercedes really undersizes the stock turbos. Regardless, the W205 C63 AMG is going to have plenty of tuning potential.
To get a preview of the motor, check out the BenzBoost report from last year showing what one should expect out of the new M177 V8 motor. The motor will have Mercedes CAMTRONIC which is an answer to BMW's VALVETRONIC and have top mounted turbos. Basically it will be two M270/M274 four-cylinder engines put together resulting in a top mount turbo configuration. This likely will allow even easier and likely larger turbocharger upgrades than the M157 due to the turbos not being confined to a location with little room. Additionally, the shorter manifolds should reduce lag in a similar manner to the BMW N63/S63 design.
It's interesting to see how far behind on this topic the mainstream automotive media is but it is nice that AMG has publicly commented on the 4.0 liter motor and what the basis for it will be.