I just talked a little to lesley. Michael has worked on the checkout process. Tried a lot of things, but it has to be postponed for the future. Surely we all know about the importance of the checkout, but there are some drawbacks, if it's changed now. If the core code is changed, a lot of modules and themes would break. That would be horrible at this point. So the checkout has to be modified with help of modules. But this also not so easy as we all know from this ps "onepage modules". They don't really work stable.
In Short: As far as I understand, the checkout will be reworked, when thirtybees breaks compability to ps 1.6. It would be too early, to do this now.