In order to both simplify our own style development, and to let the community participate in it, figure out a way to point Mapbox studio to the WMF tiles server maps.wikimedia.org rather than theirs.
I partially got this to work. There is a nasty bug in the whole mapbox stack which is hard to get rid of -- mapbox code ALWAYS expects the PBF tile to be returned in gzip format, even if it did not send the "Accept-encoding":"gzip". Kartotherian implements this hack behavior, but Varnish does not - so if tile is requested without the header from Varnish, it automatically uncompresses it.
My comment is at issue-1268
http://ns512621.ip-167-114-156.net:4000/static/osm.json gives the expected JSON, but we should generate it on the fly instead of hardcoding, e.g. /osm/info.json
If the path inside that file is to be switched to port 4000, the system would work. Or follow the instructions in the issue1268