So basically, BMG makes Town of Salem free of charge to download on Steam, and players who sign up through there can watch adverts to get a Classic Ticket. If they want, they can also purchase a "Steam Premium" bundle that functions the same as the other Premium bundles. Anyone already playing on Steam gets Steam Premium automatically. Valve also probably has systems in place to prevent account farming so by requiring free-to-play Steam players to link a Steam account, a second bot influx can probably be prevented.
I believe this would be a wise business move because the game being free to download and try out would attract more players through the Steam storefront, and those who are willing to pay can buy the Steam Premium bundle, which would be the same thing as the current $5 purchase on Steam. Currently, free-to-play players can use the Web version and the Mobile version, so why not the Steam version as well?
The one downside I can think of is that the faster loading times of Steam will no longer be a good selling point, but I don't think Steam players are buying it for the faster loading times anyway.