What problem does this address?

When publishing or updating a post, users check the preview screen to see how their page will look. If might help users if they could get a sense of how their page would perform.

What is your proposed solution?

• when users preview a page, send an API request to the Lighthouse or a similar API with a preview URL
• unpublished posts could be previewed with a temporary token, or left off
• visually display a simple score for the page, perhaps linking to the full report

Questions

Does this type of feature belong in a plugin? I would love to hear from the project maintainers if they think this type of feature can be built into Gutenberg directly or is better served by plugins? I believe existing filters would provide everything a plugin would need to add such a feature.