What problem does this address?

With more emphasis being put on content within the site editor its becoming increasingly important to highlight the boundaries between template and page/post content.

When editing an empty page via the site editor the Post Content block is essentially invisible until you select it in the layers panel. This puts the user at risk of adding content to their template rather than their page.

What is your proposed solution?

The post block should always show a prompt via an empty paragraph block. If post block is empty we can also include a quick link that opens up the patterns inserter. Eventually this link can tie into whatever is designed for the new page flow.

cc @WordPress/gutenberg-design