Yuri, you mentioned that we we're seeing a 2x decrease in payload
traffic as a result of this change.

When you profile against a sample of our traffic data does this
increase/decrease/stay the same?

Best if Yuri speaks to this. That said, as I recall, Yuri ran random page samples (or maybe it was representative samples), looking at the impact of the preexisting image library compression on the included page images in those pages versus the more aggressive image library compression (that is, what's now possible with an image quality paramater) on those images.
Zero team, what is our target device matrix these days and how robust
is its Javascript support?

My perspective is anything that will handle HTML. On some partner networks 30% or more of the pageviews come from browsers lacking JavaScript support or are blacklisted by the ResourceLoader bootstrapping, so they don't run the JavaScript. (Sufficient) JavaScript support is definitely present on some devices - we saw that in an older ResourceLoader module used by the ZeroRatedMobileAccess extension - but it's far from universal.

Incidentally, we have discussed having a means of capturing the trendline for (sufficient) JS support; we should consider use of EventLogging or some cookie setter with cookies processed at Varnish and added into X-Analytics; this is easiest done as an RL module.

Sumanah just ran the regular RFC review on this, and the go-forward plan is this:

1. Implement rewriting of the thumbnail image tags on http://en.m.wikipedia.org/wiki/Cats for Wikipedia Zero networks starting in a week or so.
2. Then the week following that roll it out on a particular language for Wikipedia Zero networks.
3. Then the week following that roll it out across all language for Wikipedia Zero networks.

As data roll in through this gradual rollout, I think we could re-open discussion on the feasibility of a hybrid approach for the mobile web in general:

1. Always rewrite thumbs.
2. On higher-JS support devices on non-Wikipedia Zero networks, as the user nears a thumbnail, fetch the higher quality version as well.