Hi,
A timecode generator filter would be great for voice over purpose. It helps actors to take the mark and when to start their line of dialogue. Our sound engineer also recommends this and tells its the same way we do our projects for feature movie.

As kdelive is based upon melt framework i think this wouldn't be an tough to implement.

This melt command shows timecode while playing the clip:

melt foo.mp4 meta.attr.titles=1 meta.attr.titles.markup=#timecode# -attach data_show dynamic=1

You can actually choose to overlay timecode when rendering with the overlay tick-box.
I agree with it's importance and I would like to see more dynamic options like this to the template titles feature. See the feature request here:
http://www.kdenlive.org/mantis/view.php?id=643

This sounds like a pro (or semi-pro) user, and most pro users talking about timecode refer to the timecode from the source footage (i.e. VITC) and not MLT elapsed time. This is coming. MLT recently gained the ability to capture VITC from DeckLink SDI, and FFmpeg recently gained the ability to write this timecode. Also, for example, the example above melt command can be changed to burn-in the VITC by changing #timecode# to "#vitc". Now, all that is left is reading timecode. That is not really possible yet in FFmpeg, but if there is stream-level metadata that conveys the starting timecode, then we can use that, but I need to refactor some code related to parsing timecode strings.

You can encode time data into an audio channel using LTC. http://ltcsmpte.sourceforge.net/

Sounds like good news!