I have recently watched the SG presentation to WMUK, and I think the only way to improve editor retention is to watch some stories, and change the systems. I have today undeleted an admittedly rather crap article, but which was no way a candidate for speedy as vandalism, and changed the wording of one of the warning templates. (All spurred by the user pages of the dozen editors I welcomed while listening to Sue.) These are, however somewhat random activities.
As you may know I have attempted to champion simplicity in a hundred different ways, with more success in some cases than others. This together with a more welcoming culture is the key. The cultural problem is two-fold, firstly systems are more abrasive than we would like, template wording etc, and secondly some editors are less welcoming than we would like. Most of this is for good reason, mainly dealing with years of vandals and trolls, but it has to change - and in a way this would be a reversion to earlier culture, though there never was a golden age, there was certainly a more vociferous party urging us down that route.
How can we promote this change effectively?