Will the Rules Task Pane return or will it always be the separate Rules tab? I have several issues with the way it is now:
Having the Rules in a separate tab causes me to have to switch back and forth a lot.
It's like having the "Show all" checkbox checked all the time. If I had a lot of rules, this might be an issue. Maybe Rule groups or views? Grouped by control? Allow me to order them?
There is currently no way for me to see what are all the rules applied to a specific control (maybe add it to the bottom of the control properties?). Debugging would not be fun.
Can't resize the controls from the Property control yet but the buttons are there, so it looks planned. Also, I can not Save or Publish.
If I am unable to start in Responsive and then switch to Classic, this is another problem due to new requirements that may come from stakeholders. I understand the differences between each but it unfortunately doesn't change the reality.
Those are my quick hits. I do like the json output, Pages, and the options on the Rules tab (On load, on change, on submit). Hope this helps!