Ok! Digital Goods is still in limited preview. There is required functionality that is currently missing in order to move Digital Goods from limited preview, to preview, to general availability. One of the missing blocks is deciding on an approach for attribution on non-monetised channels. In the limited preview, developers are required to whitelist broadcasters for installation. This whitelist should only include monetised broadcasters.
If a non-monetised broadcaster installed a Digital Goods enabled Extension today, and purchases were made on that channel, the revenue that would go to the broadcaster stays with Twitch. This is undesired, and is part of the reason why more functionality is required before enabling this program to move out of limited preview.
Hopefully this helps!