There's three possibilities here:

1. They always intended to add the new 'explicit' category, and the recent 'adult' app purge was a stupid and ham-handed way to force developers to change over. 2. They are rapidly back-pedaling after seeing the hue and cry that arose from the app purge. 3. They're not going to do it, and this is just a trap for unwary porn peddlers.

Personally I think #2 is the most likely, but none of these are particularly flattering for Apple. At the root of it, they were either being malicious, stupid, or some mixture of both.

Plus, no matter which one it is, Apple owes an apology to the developers that had their apps pulled. Suddenly pulling the rug out from under your developers is a bad business practice, no matter who those developers are.