Answering questions from the questionaire doc here.
Yes. It provides access to the clipboard (protected behind a Permission).
Possibly. The clipboard can contain any data, which could include passwords or other sensitive information. We've already released the text-only version, but now we're expanding to some image types.
3.3 Does this specification introduce new state for an origin that persists across browsing sessions?
No.
No.
3.5. Does this specification expose any other data to an origin that it doesn’t currently have access to?
No.
No.
No.
No.
3.9. Does this specification allow an origin access to aspects of a user’s local computing environment?
Yes. It provides access to the system clipboard.
No.
3.11. Does this specification allow an origin some measure of control over a user agent’s native UI?
No.
No.
No.
The same as outside of incognito.
The API does not persist any browser data, but note that the API can be used to write data to the system clipboard.
3.16. Does this specification have a "Security Considerations" and "Privacy Considerations" section?
Yes.
No.
This API is only available in Secure contexts
A Clipboard permission is defined so that the user agents can give the user control over which sites can use this feature.
To prevent malicious images from being placed on the system clipboard, the spec recommends that images be transcoded.