new feature all chat is visible to spectators?

There's been an option to view chat from spectator mode for a long time but i can't say I've ever seen it actually work. Unless every game I've spectated no one has ever used it.

Been around a long time. I don't remember if it uses your normal setting for using all-chat, or if it has a separate one specific to spectate mode, but you can enable it one of those ways. There are just a lot of games where nobody even uses all chat, so I'm not surprised you may have just not seen or noticed it until now.