It does not seems to slow down much. New members per day will decrease naturally but the main thing is that posts per day is stable. And how much cryptotalk is spending to keep their forum alive. Below is the rough estimate
Pay per Post = 1000 Sat
Daily Posts: 6387 * 1000 = 0.06387000 BTC approx 510$ paying daily
Total Posts: 84384 * 1000= 0.84384000 BTC approx 6,724$ has been spend so far in approx 15 days
It's only the money they spend for encouraging users to post in their forum. They are paying much more money to bitcointalk signature campaign participants .
Once they stop paying people for posting in their forum, the number of daily posts will significantly decrease.
Anyway, cryptotalk is a new website and they normally need advertisement. Their advertisement on bitcointalk can be effective as it makes many people know them. We don't know what will happen in future. They may be able to attract good users. But I don't know how they treat spammers in their forum. If they pay spammers, they harm their forum.