http://www.killingfloorthegame.com/2009/07/21/heavy-metal-free-content-pack-coming-soon/
Katana? Yes please. :)
Game is coming to retail soon, apparently, I think I will get it.

Nice one. It's another reason to get the retail version ASAP.

Pre-ordered it through steam, had fun in the shitstorm that ensued with a late release.
Expect the content to be buggy and require a patch.

Buggy how? Should I wait for a proper patch?

Don't listen to him, the game is in a fine state at the moment and I see no reason the extra content would cause bugs. If it does I expect it'll be fixed quickly, as I understand Tripwire have a very good record for supporting their games.

Don't know exactly how, I know that day of release many people couldn't connect to a server, if they could they couldn't actually do anything. Apparently an hour before release they realized the servers didn't work at all, and delayed the release by four hours without telling anyone when it'd be fixed, mostly because they didn't know when they'd be fixed.