Even if the offer is appealing, this is unlikely to happen. Confluence who used to offer it, has stopped and soon everyone would need to use the cloud version. The thing is that for a collaborative tool like Notion (and others) being Saas, and in the cloud is kind of mandatory. As you need your tool to integrate with other services and thus, can't be static.

The only possibility left is "dedicated storage". That works for static ressources. But the `page` content itself is dynamic and changes often, so you will need more than "bring your own S3" and something like "bring your rds" but that starts to be pretty complicated. Quip though still offer on prem AFAIK.

At the end of the day, the issue with collaborative tools, is that you can't e2e encrypt easily, and almost impossible if you offer full text search. The best solution is to trust your provider for data security. And use maybe some daily backups in your own network.