I know for a fact that about 200 BTC has been lost... A few friends of mine started mining back when mining was REALLY good. And well one, lets call him JOE, reformatted and reinstalled his computer, forgetting to backup his wallet. Then the other friend, lets call him BOB, had to leave for military training. Well BOB asked JOE to house-sit for him. BOB told JOE that he had backed up everything and that JOE was free to reformat/reinstall his computer. Well BOB didn't backup either. JOE had something like 70 BTC and BOB had around 140 BTC. So I wonder how much of that 6.534 mil. has been lost?!?
IMO: Attrition is a problem, but it is a problem that the community has plenty of time to overcome. Unlike fiat currencies, as money is lost, it is lost forever (probability wise). You won't find it; you can't print more; consider it the 'angles share'. However as soon as a certain percentage has been removed from use through, crashed hard-drives (with no backups), fire, flood, or any number of possibilities, there will be plenty of time to migrate to (lets say) version 2 over a period of years to give everyone the chance to change over.
Don't consider this 'printing more', but maintaining the 21 Million BTC, which in reality is 21 Quadrillion units of 0.00000001 btc by replenishing what has been lost through attrition...
Best Regards,
The Bear