I'll believe it when I see it. They said the same thing multiple times regarding policing behavior in World of Warcraft. In Vanilla and early Burning Crusade WoW, they actually DID police behavior regularly. On my server (Skywall), I saw many people get suspensions for bad behavior and sexist/racist/toxic chat, including a few of our own guild members (who were then no longer guilded). I, myself, got a 72 hour time out for being particularly nasty to a guy who was purposely griefing me on Netherwing Ledge.
As soon as WoW skyrocketed in popularity, GM policing simply died off. The community became absolute shit not long after. There were no penalties for being a complete troll or asshole in Trade chat or General chat. It took multiple expansions before they added the auto-mute after report function and several more before they added auto-squelching for users who were frequently reported.
In essence, Blzizard decided it wasn't economically feasible to pay for GMs on their cash cow MMO to continue to police users. I just don't see them spending money to properly police users in Overwatch. At best, it's just going to be a stricter auto-ban, auto-mute function that will likely be abused. At worst, nothing will really change.