It's a great idea, we should also break into people's houses and banks and burn any money / throw away gold, paintings, heirlooms, etc that they haven't used for awhile.
lol. That is the problem with this solution; which has been discussed here for years now. It is simply not possible to determine which coins are lost. You would be awful pissed if you opened your retirement wallet and found it empty because someone thought you weren't using bitcoin enough. Besides, we don't need them. Even if only one bitcoin was left we could use smaller units.