Specs
Mac OS X version 10.12.1
8 GB RAM
2.7 GHz Intel Core i5
Subform version 0.0.0 8afa768 on Darwin 16.1.0
Datasets
Just a couple of minor things that are bugging me when using datasets. When you select a text field and create a new datum, it doesn't automatically change to the 'New datum', it requires another click to select it. And then also it would be easier to be able to just double click the datum to start editing that text.
Duplicating objects
When you duplicate an object, the new one appears below the master (as expected) but the selection is on the master, not the copy. I'd assume if you're duplicating an object it's because you want to create something similar to the master but most likely wish to edit it too.
Layers
If the layers are collapsed and you select an object on the page, it doesn't highlight which group of collapsed layers it's nested within. This means you have to go through and open them all until you find the right one.
Again these are all minor UI improvements and I know you're currently thinking about the much bigger picture in terms of the layout engine etc but just wanted to log them so when you do update the UI hopefully these will get addressed in some way.