Half-Life mods.com have posted a new interview with them...you can check it out here.

Timmay: What is the general storyline of Sven Co-op? (For those that don't know too much about it.)

Sven Viking: Sven Co-op has no single storyline, but rather is a base for any number of storylines. Each map or map series can have its own story, theme, and atmosphere… our mapping and replacement technologies (per-entity model replacement, per-entity sound replacement, etc.) allow for some very unique maps.

A lot are set in the Half-Life universe, but there are maps that cast the players as superheroes in a cartoon world, as adventurers in a medieval RPG, as crew members of an intergalactic trading craft, etc. etc.

Sven Co-op for Half-Life 2 will take this even further, although we won’t be concentrating on replacement technologies until after we have the basic gameplay features in and working well.