It would be very helpful to have a customizable toolbar instead of being stuck with the default. Everyone uses their own mixture of features, so why not make the toolbar work for everyone. Let us decide what is most prevalent, and what order it appears. I don't often use several of the tools that are easily accessed by default (Fill, Shapes etc.) Plus why does Selection get to take up 3 slots? It's a waste of real-estate. However, I'm constantly using the tools that you've hidden behind the >> button at the bottom. (Darken, Lighten, Warp, Sat., De-Sat., Sharpen). Coming from the iPad version, these were much easier to get to, now I keep forgetting where they are which disrupts my work flow.
What features would you like to see in Pixelmator Pro?