We have a use case for this, but it would be Port writing back to Notion instead of Port gathering data from Notion.

What would be nice is to map columns from a Notion database or properties from a Notion page to entity properties of Port. The use case it would support is documenting externalized APIs where some of the data is automatically extracted from the api spec whereas the rest of the data needs to be populated manually as it concerns endpoints that are still in design and not present in the API spec.

Notion is a preferrable source of truth in this case because of the different roles of the contributing people involved (designers, product owners, managers) and a lot of their work already happens in Notion so it might be more difficult to get them to use another tool.