Valve says video game developers ‘shouldn’t offer a Season Pass’ if they aren’t ready to clearly communicate what’s included in the DLC.

You shouldn’t pre-order games, but people do it all the time anyway. Increasingly, people have gotten in the habit of pre-ordering DLC too, paying up front for content that won’t be delivered for months or even years,

Steam's new policies require season passes to specify content and release dates, with refunds for cancelled DLC.