Same typical 3-box design, with the C-pillar being butt ugly. Suspension will be absurdly high, killing whatever is left of proportions, and that's about it really. The day that car companies will murder 80% of marketing firms out there, dump focus groups will be the day when US market will get interesting.
I think the Corolla Axio with a different exterior would be sufficient. Just bring the Auris over as the Corolla Liftback to target the people who want something more... interesting than the sedan, as well as something to replace the Matrix with (like the Yaris' European-designed liftback and Japanese-designes sedan approach). They have Scion to cover for the younger market, either ways.
The Auris and Yaris are hatchbacks not liftbacks. They should have brought the hatch to the States if there is a demand for it. Toyota always plays it safe and by the numbers, if they think a hatch would not sell good enough they just wont bother