@barsanuphe: Both CM and the Calibre Plugin only understand the legacy json schema, so, yeah, unless you also think of something to do with an export inside LibrarianSync itself, yeah it'd probably be more useful in the other format

.
(Granted, the interaction with CM might not be terribly useful, but the Calibre Plugin features a GUI to manually manage the collections, which some people find useful).
I haven't yet checked how it behaves, but, FWIW, the exact filename CM & the Plugin expect is [/mnt/us/]system/collections.json

.