@pqks I do not believe this is possible at the moment. It appears to in fact be supported by the underlying text editing widget Scintilla, so it could be added to Geany, but it would require someone interested in implementing it.
@elextr I guess the idea is that you can then turn off highlighting the whole current line, which could be annoying/distracting, and still see an indication of the current line. QtCreator does this with the default theme and it does look a little nicer, IMO.
Anyway, closing as a duplicate of #844.