The other day I've found this web site: https://blog.cryptographyengineering.com, and it seems to be using a managed wordpress.com instance with a custom domain.
If you look at the bottom right corner on some article, there's a subscribe button, and I actually think Wordpress has nailed the experience here, and we just need to shamelessly copy it:
Wordpress subscription panel
So, they let you subscribe with an email, or with your wordpress.com account if you have it.
It's nice they also show the number of subscribers — great for engagement I think.
And if you log in to your wordpress.com you get some nice features like the list of notifications, a better "logged in" state, consolidate all your subscriptions in their "Reader" web app, comments, and so on.
Logged in with wordpress.com
Menu options when logged in
But none of that is mandatory. You can just subscribe with an email, and be done with that:
Message after subscribing with just an email
If you subscribe to too many sites without confirming you get this message:
Message after subscribing with just an email to many sites without confirming
So here they let you manage your subscriptions with just an email, doing the plain old sign in with a magic link:
Manage subscriptions with email
Notice that all of that happens within wordpress.com domain now.
After you've subscribed with just an email, they don't track your login state, so the subscribe button will be always available. Although they could improve this by using a cookie, and show that the user is already subscribed.
So, you do get a wordpress.com implicitly after you confirm the subscription, but it's not getting in the way too much.
I suggest everyone to play around with this flow. I think it's quite nice.