hm, it's sad that you go on and create your own solution instead of relying on a existing one

>We could, as was suggested, help out instead with Rules and make sure folks can port their code from Workflow-ng to Rules...

I think you got something wrong, there will be a straight upgrade path from workflow-ng to rules supporting even changed conditions/actions.
Of course there was also an upgrade from 1.x to 2.x - I don't noted that ubercart has troubles with workflow-ng 2.x - which can't be really serious as workflow-ng 2.x is nothing more than a little improved 1.x version, which is of course compatible with it. If you'd have contacted me, I'm sure we would have been able to fix the issues.

About UI integration:
* Rules comes with a well founded API - so it would be no problem to create your own UI on top of it.
* I think it wouldn't be hard to integrate in another place the existing UI either.

Rules comes also with a new concept: Rule Sets, which could be compared with subroutines.
They can be used for customization, so you don't need to create events when there aren't really one. Instead you could ship with a default rule set, which users then can customize by adding/changing rules.

Anyway it looks like the decision has been made