My current wishlist (all for Windows platform):
SU: add API methods for manipulating the behavior of the trays (checks if open/closed / open / close / flyout-time / autoclose). Also; the current keyboard toggle is not a toggle if a tray is docked to the side. It doesn't do anything.
SU: add API methods for creating custom stacked tools.The current 'getting started' toolbar has nice dropdowns for several commands. It would be nice if that functionality was available for plugin creators as well.
SU: add API option to give a section cut a name so you can easily pick it by name
SU: scale section planes (when making them visible) according to what's currently visible instead of by the boundaries of the model (with lots of hidden objects).
LO: there's a few years old (and reported) bug that if you right-click a SketchUp view sometimes it doesn't show the current scale for that view. Also, sometimes if you set the scale by using right-click it switches to the next scale in the list (choosing 1:100 sets 1:200).