All too often I find too much screen real estate is gobbled up by menu/tool bars. Sure you can disable some and customize others, but sometimes I just wish they weren't there!!!
So, here's something I'd like to see (or not see). No menu bar and no tool bars. Instead you call up the menu/tool bar(s) with a R/L-Amiga + Mouse click (or for users with mice having 3 or more buttons, assign dedicated button(s) to call up the menu/tool bar(s)), in much the same way MagicMenu does.
Can't think of anything else at the moment.