Zach: We should figure out if "billingAddress" is the right label for this, or if we should make more generic as "vat". We need to spec out the behavior change, since this probably won't require shipping options."
Payment option filtering; pull request from Rouslan relating to filter/capability matching by the browser.
Payment Method Identifiers
Proposed changes to PMI spec. Adrian updated since last week, including a tweak in intro to section 3 of PMI spec to clarify how PMI is used