OK -- under control for now. DISCLAIMER: everything is subject to change, as it was before when accessing undocumented REST resources.
The short answer is you must now include an 'X-version: 2' header in your request headers, or add 'v=2' as a query param. When you do this, it is supposed to work for any endpoint except one (can't recall which), but I updated my module to use v2 only as needed for specific endpoint patterns.
The other important finding is that the data structure returned for the v2 API is different. Instead of items being a subkey of data, it is (for now anyway) a top-level key. I also had been checking the status key (copy of the HTTP response code), but that was removed.
I am still working on updates to my scripts, but the netflow script is working again. I will post my revised LMAPI.pm to github when it is stable.