Numberical/decimal textfield styles
This is "so easy" to code yourself to your own purpose using SetGadgetFilter, it hardly seems worth it...although I concede it might make it marginally more beginner friendly.
I'd also agree with the Notify() request, and the "table" or "Listview" gadgets (including icon support).
Personal requests that relate to the CE IDE that I can think of:
TextAreaX/Y
Obtain the current cursor graphical x & y from a text area, and / or the graphical x,y position of a given character in a text area. I realise this is almost certainly limited by the underlying gadgets.
FontWidth
Return the width of a fixed width GUI font (so that tabs in textareas can be set consistently!).