The Metro: Last Light forums translated video interview by Ukrainian site itcchannel (which NeoGAF found), where creative director Andrew Prokhorov confirms a PS4 version of the game, DLC and a standalone multiplayer game to arrive soon.
Firstly, 4A Games are planning an SDK release, which will be with the multiplayer. The latter is releasing as a separate project, most likely an Xbox Live Arcade game and will see release a good 6 months after Last Light.
There will also be five DLC story missions from different characters’ POVs. 4A Games clarified that this wasn’t cut content and is actually additional content. A Season Pass is also looking likely.
Finally, the developer is planning a PlayStation 4 version of Last Light, though it’s unknown when it could release. Prokhorov gave an indication that will be “with Metro 2033”. This could mean that both games are getting the next gen treatment.
Metro: Last Light will be releasing on May 14th for North America and May 17th in Europe for PS3, Xbox 360 and PC.