As we've built out the set of block types that we currently have, we've just added them to the grid. Here's what that currently looks like:

The Block Library UI (aka Inserter) itself will need a restructure as soon as we have more than ~12-15 blocks. For now, we should consider organizing them, either by how commonly used they are or by type:

Order based on the last usage data I've seen

1. Paragraph
2. Image
3. Heading
4. List
5. Video
6. Separator
7. Quote
8. Read More
9. Page Break

Group them roughly by type (text, media, other)

1. Paragraph
2. Heading
3. List
4. Quote
5. Image
6. Video
7. Separator
8. Read More
9. Page Break

My preference would be to take the second approach (group by content type), but I'm open to other suggestions.