So - the migtation started a few days ago is now more or less complete.
This has been applied on two blogs
https://www.chrissearle.org - this site - mostly tech
https://www.searle.me.uk - personal site - photo/radio control/3D printing etc etc
The personal site uses more complex code oddly enough - it switched from html to rehype/htmlAst to do custom components in markdown to replace the old middleman helpers. It also uses the fluid sharp image handlers to get better image handling for the lists page. Finally it has a more complex gatsby-node to handle both categories (fixed categorization) and series (adhoc sets of articles).
Mostly I've been very pleased with how it has gone - about the only thing I still am not 100% happy with is the naming issue mentioned in the last post - to recap:
I'm not too fond of the renaming of files that gatsby-remark-copy-linked-files does for linked files - but not so much that I can't live with it for now