Ubercart

Great, was looking forward to this!

I hope we can still have the configurable products for Ubercart 4.x, (the attribute system). Although flawed, it is really powerfull for people (like me...) with configurable products.

One of the key points of difference between Ubercart and Drupal Commerce is the simplicity of creating products on the back end. Ubercart still has many more mature modules than DC, and I will often choose Ubercart over DC if I know my client is not particularly computer savy.

If you do separate products and nodes, lots of work needs to go into making the interface that manages the product and the product display node more user friendly than DC does. I think an interface similar to Drupal's Field Display UI with the "local task" style sub menu could be a good place to take some inspiration.

Merge Order-Edit and Checkout panes into one.
+1 from me.

I think it is necessary to maintain Ubercart 4 as an addition to Drupal core and not make a profile or distribution, like Commerce.
Commerce is very difficult to implement for front-end developers, because of it's "maintainability" with features and so on. That's also the reason why Ubercart is lean and mean and easy to customize. I suggest to keep the roadmap in the way Drupal 8 is going. (There is mentioned the problem that profiles and distributions are too complicated.)
and also keep the focus on resonsiveness/mobile.
Maybe some new business models as an addition to the current product options.

When something is good and working well, one should not change too much. If you really can improve something it's worth it. My general concern is that Ubercart must not go the same way as Commerce.

There is a discussion of this at https://drupal.org/node/1836900 with some good ideas.

A big thing is to make Ubercart take advantage of the new features of Drupal 8, and the big one where it can do that is with Configuration Management.