Edited: I got the wrong impression from reading too quickly. Corrected comment:

If needed we can choose a different level than 1000 karma, and change it over time in response to experience, so it's a flexible system.

However, I'm not certain the idea itself is sound. I don't have the feeling that mutual upvoting by new users is a real problem that needs solving. Can you give links to example comments where you think the proposed rule would have helped?