So long as you can switch off all those extra panels . One of the big aspects of ArtRage for me is the totally stripped back interface and simple workflow. After a day of using complex software in Adobe CC, ArtRage feels like actually picking up a sketchbook in comparison and it's more inspiring to create than get bogged down in options and work flow. Unless you're creating something that requires fixed brush widths such as ink drawing, is it not more intuitive to shift and drag to resize the brush as you work?
I agree that the scraps panel could use a little more flexibility though - it remains low res at the moment so if you're working on a print scale piece and switch to your scrap, the brush is massive.
I think been able to resize the grids independent of the reference images would be useful as it would be more intuitive for placement and scaling on the canvas.
The one other aspect I'd like to coincide with the water cleaning, is the option to have to manually reload the brush rather than it refresh colour half way through blending on the canvas.