One feature i think would be really useful is a "favorite setting tab". I'm a s3d power user and when it comes down to changing settings on the fly it's not so easy.
Let's be honest, once we get our settings tweaked out, we'll only change a few of them. In my case, depending on part i'll play with speed, layer height, shells settings, fill patterns and cooling settings.
If i'm printing the same part and i want to change a few things on the fly, i have to change tabs all the time and keep on forgetting a setting here and there. So basically, adding a tab in the FFF settings window where you can choose a couple of personalized favorite settings would be amazing i think. This would be even more useful for parts with variable settings. When you make a part that has 3 different process it can become really time consuming to change a setting in all of those different tabs.