The Waikato Expressway, when completed, will be a stunning bit of road. They do need a bit more work on SH2 from the bottom of the Bombays through to Tauranga - especially the bit through the gorge and to Bethlehem. The gorge would be very expensive to fix though, and I don't know if it will ever be done.
They are looking to push the expressway to Piarere in the next few year (politicians willing)
So I am guessing they will use the Kaimais as the preferred route to Tauranga...