Let's consider the social contracts that intellectual property protections exist to fulfill in the first place.

For trademarks, for me at least, that seems to center on preventing various harms resulting from consumer confusion, deliberate or otherwise. Indeed, merely "protecting established revenue streams" is explicitly not a reason I'd endorse.

In that context, I'm not sure the consumer is meaningfully confused or harmed by any possible (otherwise legal) use of the trapezoidal four-finger shape by a non-KitKat product. So I'd be inclined to say "no" to trademark protection for it.

Contrary opinions invited, particularly consumer harms I might be overlooking.