Just because one spec failed you are suspicious of all specs? If it solves a problem people will use it. If it doesn't they won't. Are you saying you don't think that payments are a problem that people want to solve?
I'm suspicious of specs that require long term browser vendors support. Payments are definitely a problem that people want to solve, but my estimate is that it would require 5-10 years of continuous commitment from browser vendors to solve this problem, which I doubt will happen.
What problem is it solving? What's so bad about entering my credit card details?
It isn't solving any problems. This payments API looks like a simple AJAX call. This API shouldn't even exist in my opinion.