Thanks again to Allan Jude of Klara Systems and Luke Young of bored.engineer for their very interesting comments and explanations.
(these tech notes were published in March of 2022 - they are backward looking to the events of Q4 2021)
Can you email ? I actually searched for our conversation for a while and could not find it ... bottom line is that 'mkfifo' is in place and I can't wait to craft up some fascinating remote ssh examples with it ...
For everyone else, the mkfifo command lets you transfer arbitrary streams of data between two systems while using rsync.net as an intermediary.
It makes me happy that it works.
Otherwise interesting write-up and pruning unused features I do think helps with security generally.