Mixers can promote their mixers on cryptotalk.org too but they will not get any result. Compare the traffic of bitcointalk to altcointalks and cryptotalk, I think the signature campaign run on this forum will result in far superior results compared to signature campaigns run on altcoinstalk and cryptotalk.

I think that old and well-known mixers will continue their job but it will be very hard for new mixers to rise and will probably have to spend more money in marketing because their promotion choices will be very low. Bitcointalk was the most cost-effective and beneficial way to promote bitcoin mixer. I think they'll promote their mixer on websites like zippyshare and torrents.