I was asking for a feature like this for years in FPSC Classic
One thing that i can see becoming a problem too is having these in-game drop-downs in the current UI for skybox, grass and ground. What will happen once you have 50 of each? Will some annoying scroll bar appear? I personally prefer windows UI over graphically pushed interface design. As it just works a lot better with utilizing your windows preference for text point size and etc. Also it handles overflows better. Not sure what will happen once we have an over abundance of items. Its not like we can press a letter and it would automatically skip down to it.
Perhaps that's just me but I never personally was in favor of the TAB display. Though its very well nicely designed.
i7 -2600 CPU @ 3.40GHz - Windows 7 - 8GB RAM - Nivida GeForce 420 GT