Finally got a copy of Hardie's commentary. He has some good bits in the introduction.
I've always found the question of how the Aeneid can be structured very interesting. There's the obvious split in 2 halves as a reference to Homer with 1-6 showing Aeneas's Odyssee (and his struggle with fate, until he finally accepts it) and 7-12 being Aeneas's Iliad (and the sealing of his fate).
However, you can also find the separation into 3 parts consisting of 4 books each, which I'd consider an attempt by Vergil to set himself apart from Homer. 1-4 would then obviously be Aneas in Carthago, 5-8 his landing in Italy and the preparation of the war, and 9-12 the actual war. I find it interesting to hear about the Odyssean subplot Hardie sees in 9-12, I haven't thought of that, yet.
Btw. scholars have tried to split Ovid's Metamorphoses into 12 parts to construct a certain reference to the Aeneid. While that is certainly possible, Ovid himself wrote about his epos as "
ter quinque volumina" in his Tristia - at the same point when he makes a reference to the Aeneid when he writes that he wanted to cast his Metamorphoses into the fire upon leaving (just like Vergil wanted his Aeneid destroyed after his death):
sunt quoque mutatae, ter quinque uolumina, formae,
nuper ab exequiis carmina rapta meis. (Ov. tris. 1,1,117f.)
So Ovid also acknowledges the tripartition of the Aeneid (and sees a similar partition in his own work).