The two things that a great personal knowledge base (imho) should start with.
1. Security. Just the iron-clad certainty that your data/information is secure, and it’s not gonna get deleted/corrupted, made inusable.
This could mean backups of your data?
2. Accessibility. Your information/knowledge is no good if you can’t access it. It should be always accessible.
Because it needs to be accessible, I would think it needs to be in the cloud.