Hello ! SteemPress co-founder here, Thanks for the article ! I do no speak Japanese but I have a friend who does (thanks @fukako :D)

For the SEO question, the delay feature allow you to publish first on your blog and then publish to steem after a few days (you decide the delay). Which means that google and other search engines will index your blog first and tag steemit.com as a duplicate. And so your blog's seo ranking won't be hurt.

Feel free to join us on us on the discord : https://discord.gg/W2KyAbm
If you have any more questions.

I would love to discuss more about the steemit-jp initiative.