More functionality is always good. However, at this point, I would recommend to focus on fixing bugs and defining a more generic payment fulfillment interface, rather than truly rearchitecting the whole module.
The reason is simply ACS 4.0, at which point you'll be able to have a truly modular system that doesn't bring about conflict with the rest (and you can even fork the ecommerce module!). I recommend holding off until then to really bring about huge changes to the ecommerce module. By the way, as soon as ACS 4.0 is available via CVS, we're going to start thinking about an approach to porting it.
