@fago: Hey fago, thanks for stopping by. As I mentioned above, we're very grateful for your work and don't want to discourage you from continuing to innovate and improve your system. We just had to decide whether to keep depending on an external module for an essential core feature or roll the necessary functionality into core with a system that is similar but more suited to our needs.

For example, we offer in core a basic product list and a basic catalog. Either one of these is possible in Views with much more flexibility, but we know that new users to Drupal and Ubercart would expect at least some sort of store product listing. To that end, we provided a basic solution so folks aren't overwhelmed.

However, we also provide integration so users wishing to take advantage of Views (who doesn't? ) can still do so. We want people to be able to use the best tools possible in building their Ubercart sites. However, we don't want the core of Ubercart to be restricted by an external dependency. It's just not something we can govern or troubleshoot as easily as we can a core file. (And when I say "restricted", I don't mean the external modules are inferior or incomplete, but rather they have different use cases than what we might need to accomplish in core.)

So, I still think a contributed module can easily integrate UC w/ Rules, especially since it seems we'll both have similar hook structures and requirements. In fact, I'd be quite interested to see it happen.

@zmove: Ideally, the things Ubercart needs in its core will be easier to accomplish with the new system - defining complex taxes, shipping rules, and automated order processing. We'll provide similar conditions for necessary things like checking/modifying user roles. However, for external integration that's twice removed (i,e, UC -> Rules -> OG), there would just have to be an extra step in the form of a CA action that invokes a Rules trigger.

The CA system in core uses a similar enough hook structure that UC modules won't have a problem using the new system with little conversion. I don't expect third party modules to integrate with Ubercart's CA system in their core, though they'd be welcome to do so. Instead, it would seem like a module could function as a lightweight bridge that maps CA into Rules or vice versa. I think we'll just have to see what needs/use cases pop up as the project moves forward.

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The real clincher here, too, is speed of development. A Drupal 6 version of UC is almost ready for testing, and we simply can't do that with Rules as is. It's hard enough integrating w/ complete, stable modules, much less modules that are still in alpha development.