If you find it worthwhile we could make a SF request.
It sounds like an interesting idea, but if you make a request at Sourceforge, you're wasting your time. Nobody reads them, we have not used Sourceforge for well over a year (actually.... 2 years?).
Measuring actual productivity by what you type may be hard (as
wwolf pointed out), but at least you could record what files you have open for how long, etc. to get a
rough figure of what you did. This may help yourself optimize your work process (but it is not useable as a measure of payment).
There have been many other attempts at automated accounting of "work" in the past, for example people have been assessed on the number of code lines changed per week. However, 3 good and efficient lines of code may be a lot more work and are better than writing 1200 lines of bullshit code. Thinking for half an hour may be worth more than typing some rubbish that won't work. This is not taken into account by this form of assessment.
Also, studies have shown that if people are aware of this accounting measure, they will simply push their ranking by writing bloated (and inferior) code, which leads the assessment to absurdity.
In the end, the only effective measure for "work" is to define goals (milestones) that you must reach under the constraints of the design rationale. Whether by staring at the screen and finally writing 3 lines of code, or by constant trial and error, it is the outcome that is of interest.
