I'll be...... Yesterday evening I was thinking about the same idea. However, there are a few problems. Private owners of lost Bitcoins are still the legal owners.
1. How to track which ones are really lost? That should be something done through KYC, otherwise, anybody could say for, say... your wallet, that Bitcoins there are lost. Why? I don't know? Why do people, steal, kill other people, why do they make computer viruses.....?
2. What if a legal owner finds his key one day, what then? OK, I would have been rich but they burned my 2000 Bitcoins.