There’s going to be an XProc Community Group Meeting on 5-6 September, hosted by le-tex publishing services GmbH at their premises, Weißenfelser Str. 84, 04229 Leipzig, Germany.
For more info, see https://github.com/xproc/Workshop-2018-09/wiki.
Or why not read up on the current status of the spec, at http://spec.xproc.org/master/head/.
See you in Leipzig!