Risks section discussion
Thanks for these data KrebMarkt, they are fascinating. Just taking English for simplicity they do show a decline in NEW editors from a peak of 13689 in April 2007 to 8001 in Jan 2010. That might seem a matter for concern. HOWEVER, the TOTAL number of editors has gone on rising over this period from 233,573 to 558,878. That's an absolutely enormous number of people.
The total number of monthly edits and of new articles has declined. HOWEVER, that's not necessarily cause for concern. I think there's one overriding factor to consider here. As time goes by there is less to be done - all the big subjects are comprehensively covered and editors must be aware of that. Many of them are historical and don't necessarily need updating very often.
The rewards from building up the articles in the first place are considerable - the rewards from finding minor errors and adding detail are very limited. The need is also smaller - it's like the shift from 200,000 builders of the pyramids, to a smaller force maintaining and embellishing it.
I would still like to see evidence of any deterioration in the final product before we are launched into a measure that could actually increase the errors rather than reducing them. Sure, the number of small errors introduced will creep up if no-one attends to them - but is there evidence that no-one is attending to them? Is there evidence of any rise in the errors?
More stuff:
What is more important than the potential community decline, is the lack of Editors diversity in Wikipedia.
Do nothing and that bias won't change unless you are happy with that situation.
I see that women are very much under-represented, and single childless men are very over-represented. If there were any race data, it's probable that blacks would be very under-represented. There are probably social reasons for this - the people there are most of are those with most free time alone and those with most familiarity with computers. And because of that some bias will probably always be there. These biases probably affect content. I doubt if they affect POV much, but they may affect what subjects and aspects are better covered.
It seems worthwhile to try to remedy the imbalance. However, most efforts to correct diversity imbalances in other spheres address the imbalances directly - eg by positive discrimination, or appeals directed at that group only. A generic call to "be bold" is not likely to attract women and couples with children more than single guys, and so would not improve the diversity. Are there plans to direct the call to women Wikipedia users?
Re the number of editors with 5+ edits per month declining, I see that as a normal result of the content of Wikipedia having reached some kind of maturity. To take my own example, I became VERY involved in the set of articles that interest me most in January 2010. Over the first few months I made many many edits to get these articles into acceptable form. After the basic groundwork was done, however, my rate of edits declined and now has dropped maybe to 5 per month, maybe less. If you view this as magnified over the whole of Wikipedia, the fact that so many articles are already in place, and already large, is bound to reduce the need for edits.
I was thinking to use "be bold" aimed to areas where we are severely lacks stuffs with the idea that the underrepresented population to be most likely to answer the call in those areas.
You are lucky to not edit contents related to Fiction, it's a never ending works there. From my experience my project in the English is failing to recruit new active editors with the ultra majority of the project members close to the 10K contribs and beyond. This doesn't mean there is no work to do with ratio of over 400 articles per active project members, keeping articles in line from fanboys & vandals or avoiding GA/FA articles quality erosion is complicated.