I respectfully differ on this.
I see that the Papez circuit loops through most of the limbic system (including the hippocampus) and that the hippocampus is the main mediator between the two systems (limbic and cortex) - it combines the episodic experience and what we felt about it to drive judgement. We do NOT think through what is good and bad about things, we feel it first and remember it with the experience. This ranges from simple objects to complex social settings. Our judgments of good and bad are the accumulation of a multitude of impressions, good and bad, about everything we have ever experienced. The few cases of humans without a functional amygdala (a huge contributor to efferents to the hippocampus) show a profound lack of judgement. You do NOT want a powerful AGI that is not able to exercise good judgement. Some artificial replacement would likely be so alien that humans would have a very hard time understanding why it did anything.
LIkewise, the lower-frontal-lobe is driven with efferents from the hypothalamus. You can say a lot of things about cortex but one of them is NOT that it initiates actions. Cortex is passive. The sensory stream and the motivation/action drives all originate from outside the cortex. The sensory part is self-evident, the forbrain part is the hypothalamus after it experiences whatever is signaled up the brainstem and by taps in various parts of the cortex - primarily the temporal lobe.
The cerebellum does coordinate action going down the brainstem to the body but for humans, serves the very important function of driving the unfolding of activation in the forbrain that is routed back to the upper levels of the WHAT/WHERE streams, the bit we normally call thinking. This is also critical to the learned motor actions we call talking, closely related to this thinking bit.
I know that newbie AGI experimenters think that they will just copy the cortex and voila - they will have a functioning AGI - or at the very least - that these subcortical structures are little stubs that they will tack on the fancy cortex. I say that this shows a profound lack of understanding how much of what we are is tied up this these subcortical structures.