The first working draft started circulating mid April but there are plenty of revisions still to come. The payment processes specification proposed by the W3C will play a large role in eCommerce, and IoT if the payments processing market remains as fractured as it is today or it could be mostly ignored if a large player can move its way far enough down the web stack before the spec is released.
The Web Payments IG has only had the opportunity to review a handful of the 40+ use cases, 120+ requirements, hundreds of pages of payments research submitted to the group via various other standards group output such as ISO20022, research documents from X9 and the US Federal Reserve, documents from the Web Payments Community Group, and input from the general public. Our desire is to align with the larger payments industry when it's possible to do so. Expect this document to be rapidly iterated upon with that desire in mind.