Looks like Strapi has paid only features. Are these significant to most sites?

https://strapi.io/pricing-self-hosted "Free...Up to 3 default roles"

https://strapi.io/blog/introducing-strapi-enterprise-edition...

Sanity.io doesn't seem to be fully open source: https://github.com/sanity-io/sanity/issues/978

"You can only run the Studio connected to the Sanity hosted backend. There is no option for connecting the Studio to another backend."

I'm using it. The docs leave a little to be desired if you're customizing (they just released a new major version), but you can customize and replace the rich text editor with your own, add a preview button, add a deploy button, etc.

If you want a wordpress replacement though, there will be a big learning curve as it's a general-purpose CMS, not specifically for blogs.

StrapiCMS is MIT licensed and any role limit could easily be mitigated.

https://github.com/strapi/strapi/blob/master/LICENSE "* All software that resides under an "ee/" directory (the “EE Software”), if that directory exists, is licensed under the license defined in "ee/LICENSE"."

What features does that impact?

strapi is an exciting project that is trying to do too much, but I don't think they are a good alternative to WordPress. They need to stop adding features and start making it work stable.