I suspect some people would be inclined to stay if the service or an alternative were provisioned at a level similar to that of the Optus L3 offering, enabling you to offer a lower per-MB price. I would also welcome some commentary about why Optus wants to force people to their L3 product which presumably is more expensive for them to provide.
In a more perfect world, one should be able to choose from a selection of ISPs regardless of the mobile (virtual) network operator chosen rather than the more restrictive situation that exists today.