It would be really interesting to find out what portion of the new publishers and what portion of the baptized are born-ins as opposed to converts. In English US and likely majority languages in EU countries and Japan, I would guess based on my observations that the overwhelming majority of the growth are coming from born-ins. In the 3rd world countries and non-majority languages in the industrialized countries, I think there is still a good amount of convert growth.
Because of this, I would imagine that there is enough growth in the 3rd world countries still to offset any retention issues and lack of converts in the industrialized countries. Only when the convert growth slows down in the 3rd world countries will we see a decrease.