I feel haven's reception on steam could go well, especially if they don't monetize it through steam. Several games on steam are free, yet still have avenues for players to purchase/subscribe to content (see planetside 2 and realm of the mad God). Some players will hate the game, some will love it. At the end of the day, if 10000 people try haven, and only 1000 stick, that's still 1000 new members.
The one main problem I see with releasing haven on steam is the default client. It's come leaps and bounds this past year, but it's still sub optimal for the general population, especially as the introductory client to new players. Devs always say "why bother updating our client when the people use custom? We'd rather devote our time to content". While this is a perfectly understandable frame of mind, the default client is the first impression made on every new player of the game, and having an accessible, user friendly client is more important than having loads of content or activities. You simply can't access all the content a game has to offer if you don't know how