I see your idea and I suppose there is value in it, but the problem of screen sharing is basically fictional compared to the real problem of someone just uploading company data (+ metadata!) to a random service some random person came up with.

Screen sharing only shares pixels and does so through parties that the economy considers trustworthy enough.

This is not going to work as the SaaS you seem to envision it to be. It might work for a self-hosted internal service thing or a group of friends though.

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Thinking about this, I suspect that at least one naive bored corporate guy browsing HN will have tried this out with a random pptx they had lying around on their work computer. The data is now.. somewhere.

So this could be an actual honeypot.