Polyfills/Wireframes for the browser API proposals

At this stage it feels like working examples of how the UI and flows would
work and tie together would be very valuable in understanding the
implementation options for the two proposed browser APIs.

Is there anyone in the group that has built a polyfill for either of the
API proposals or is planning to do so in the next few weeks before the f2f?
If not, is there anyone that would be keen to give it a go?

I am aware of at least one polyfill in development for the paymentRequest
proposal, is there one available for the Web Payments CG proposal?

I have started building some wireframes of the UIs I envisage based on what
has been proposed to date. Is there anyone else working on wireframes or
interested in assisting with this work?