CVG had an interview with the developers of S.T.A.L.K.E.R. and learned that they will soon release a big update.
This update will add a new game mode called "Freeplay":
"We're preparing a big update with a new game mode - Freeplay, with no story tasks, including only the A-life driven ones, where the goal is to gain ranks, climb up in rankings, so as to become the best S.T.A.L.K.E.R. in the Zone."
When we're to expect to update wasn't revealed, but speaking about the future of the game Bolshakov did mention too that, now the multiplayer SDK for the game has been released, the developer's working on getting the single-player SDK out the door. So take note, mod creators.