rolandtanglao.com (@firstname.lastname@example.org) thanks for the kind words and yes I was at W3C TPAC in Vancouver, would have been nice to chat!
You’re right, neither ActivityPub, Webmention, nor h-entry for that matter have any explicit length limits.
You can run “an experimental 10,000 character limit AP implementation” on your existing site rolandtanglao.com with a few webdev steps:
Setup Bridgy Fed support on your site:
* https://fed.brid.gy/docs#setup (SSL, /.well-known/ server redirects, homepage h-card)
Add h-entry + h-card markup to your post template:
Then send Bridgy Fed a Webmention when you publish a post.
Presto, you’re running an AP implementation without a character limit!
Happy to help with any of those steps. Drop by https://chat.indieweb.org/dev!