Support for multiple cursor in GtkTextView/GtkTextBuffer
Multiple cursors is very useful when you need to e.g. insert the same text in consecutive lines.
The same nowadays can be addressed with find/replace and regex... but it would require a lot of key strokes and depending on the application using GtkTextView even mouse clicks.
I'm not sure if this could be implemented in GtkSourceView without any changes into GtkTextView, if so, let me know, since this is something that would fit better there.