I've seen JSON downloads for WL. Google is your friend.
Really? Where? Some users may have accessed the XML and forwarded the data in JSON, but I've never seen direct-access mention of JSON (not to say that it doesn't exist, but somehow I think it would be more prominently described somewhere). Anyhow, JSON vs XML, does it really make much difference which approach you use - they're essentially different grammars for the same thing?
The wl URL syntaxes are not that well documented. I only found the xml one because it was posted in this forum.
The archive record download is fully documented in the Serial Tech Ref document, which is the standard place to look for Davis API details. The XML isn't described there because Davis don't formally support its use. I don't honestly know whether the XML is available for Connect uploads but I guess it probably is, in a more limited form possibly and showing the latest data plan interval upload.
Edit: Actually I've just checked on one of our Connects and yes the XML is there.