The things that annoy me a little about CA is that, all "non ubercart related" features needs to be programmed.

Simple real recent example : I needed to check some informations about the user to calculate tax, especially user roles. In 5.x with workflow, it was possible through the UI. With CA, I had to hack the core to write some conditions related to users for orders. Ok, it was simple, it was quick, now it's done it probably will be added to the next release but, imagine you will have to rewrite for CA all conditions, actions that could be already integrated into rules.

And a module maintainer will that would want to add some trigger / conditions / actions functionnalities to his module will probably write an integration with Rules, not CA, because CA is only related to Ubercart whereas Rules already have lots of modules integration.

After that, I didn't look in the Rules code to see how it's done, I just saw that it was pretty simple to write some things for CA cause I wrote some users conditions, maybe this is a Nightmare to write things for Rules. But I know that I think the total amount or work will be higher if you want to write all features of rules into CA than integrating Ubercart conditions/actions into rules. But in the first case, the task is for Ubercart team, in the second case the task is divided among modules maintainers/Ubercart users...