I know this is a very complex feature request and is not going to be implemented anytime soon, but I thought I add it to the tracker so it is at least there.
What I would like to request is a Rich Text Edit window, i.e. a textbox that allows the user to input text and allows that text to be colourised. That is, it should be like CEGUI::MultiLineEditbox, but allow to colourise the user's input inside it.
Background: In TSC, we have integrated a scripting engine based on mruby which allows level designers to enhance their levels using some scripting. For that, we provide a script editor window in the level editor, which is currently implemented by means of a CEGUI::MultiLineEditbox and thus looks fairly mono-coloured. We quickly received a feature request to implement syntax highlighting, but this is currently not possible.