I've been following your ssh blog articles, thanks for them they've been a good read!
Whilst running through these steps I encountered a problem with converting my newer style ssh key to PEM format. It wasn't immediately apparent as there was no error or output when i did the conversion using the -p option you used in the article so I just assumed it had been converted and moved on in the steps.
It seems that it's not possible to change ED25519 key types to PEM format:
$ ssh-keygen -e -m PEM -f .ssh/my_special_key_id_ed25519
do_convert_to_pem: unsupported key type ED25519
I couldn't find anything about this error, just wondering if you had any ideas?