For those who are interested, Python for Kids 2 has been completely rewritten as LaTeX (using No Starch's style); partially in text files, and partially in Overleaf:
Overleaf was great, particularly for the review process, but I have to say working in LaTeX is an order of magnitude better than using a Word Processor - especially when the files are backed by a git repo (which Overleaf provides) so tracking changes is easy (looking back at the history of changes in a file to see what I changed, is a big win).
Can't comment on how No Starch's editorial staff found working in Overleaf (because we haven't really discussed it), but for me it was all positive...