One of the games that I've played and been involved with, DUST 514, started making their roadmap public over a year ago via a Trello board, and it had a huge impact with the players. The same company, CCP, has just announced that their roadmap for EVE: Valkyrie is public as well.
If you're committed to your customers, there's really no downside to doing this.
If you're committed to your customers, there's really no downside to doing this.